Solid state ionics: advanced functional materials for solid state devices

Resume : Oxide materials play a prominent role in emerging and evolving advanced functional materials applications such as batteries, fuel cells, sensors, and separation membranes. A major limitation is that cost-effective production methods of most oxides result in polycrystalline materials. The resulting grain boundary (GB) regions can differ substantially from the bulk material both in composition and structure. This is further complicated by the localized charges of oxide bonds, leading to local variations in charge while still requiring the preservation of electroneutrality globally. The end result can include vastly different properties at the GBs than in the interiors of the crystals, often reducing performance. Also, GBs are not homogeneous. While valuable information has been learned through studies of artificially produced periodic two-dimensional GBs, the materials used in actual applications predominantly have three-dimensional, random high-angle GBs. Therefore, the quantitative characterization of the 3-D GB nature is indispensable for the understanding and development of advanced functional materials. Several analytical techniques have been applied to probing some aspects related to GB composition. However, limitations have prevented the full realization of the desired 3-D characterization at the necessary size scale. The most common method in recent years is high resolution scanning transmission electron microscopy (TEM). With continued improvements in aberration-correction capabilities, this technique is unsurpassed in imaging the GB structure, particularly for well-controlled GBs and interfaces, such as bicrystals [1-4]. However, quantification in TEM using spectroscopic techniques, such as electron energy loss spectroscopy (EELS) and energy dispersive x-ray spectroscopy (EDX), can produce misleading quantification results, even for a single crystal of known composition [5]. Also complicating quantification is the low atomic mass of oxygen and its subsequently low characteristic X-ray transition energies [6-9]. Consequently, compositional GB analyses using EELS and EDX typically provide 1-D or 2-D projections of semi-quantitative information. The challenge in measuring 3-D variations, particularly in oxygen concentration, over such a small region makes atom probe tomography (APT) one of the only methods available for direct quantification. APT analyses have demonstrated the ability to identify local 3-D chemical variations in nanometer-sized structures. For example, APT has shown segregation of solutes [10-11] and impurities [12] and precipitate formation at GBs [13] in metals. More recently, APT measurements of impurity and dopant segregation at the GBs of oxide materials have been demonstrated [14-16]. In this talk, the application of APT to quantitative analysis of oxide grain and phase boundaries for a number of different functional oxide materials is presented. In particular, the ability to relate the nanoscale measurements to processing conditions and/or macro-scale properties, such as conductivity and capacity fade are discussed [17-18]. This includes the discussion of both the advantages and limitations of APT for these analyses and the opportunities for correlating APT with other characterization techniques [19]. [1] H. Hojo et al., Nano Letters, 10 (2010) p. 4668-4672. [2] Z. Wang et al., Nature, 479 (2011) p. 380-383. [3] B. Feng et al., Applied Physics Letters, 100 (2012) p. 073109. [4] K. Song et al., APL Materials, 2 (2014) p. 032104. [5] G. Kothleitner et al., Physical Review Letters, 112 (2014) p. 085501. [6] M. Aoki et al., J. Am. Ceram. Soc., 79 (1996) p. 1169-1180. [7] Y. Lei et al., J. Am. Ceram. Soc., 85 (2002) p. 2359?2363. [8] T. Nakagawa, et al., J. of Mater. Sci., 40 (2005) p. 3185-3190. [9] J. An et al., Sci. Rep., 3 (2013). [10] J. A. Horton and M. K. Miller, Acta Metall. 35 (1987) p. 133. [11] B. W. Krakauer and D. N. Seidman, Rev. Sci. Instrum. 63 (1992) p. 4071. [12] Dieter Isheim et al., Scripta Mater. 55 (2006), p. 35. [13] S.P. Ringer, K. Hono, and T. Sakurai, Metall. and Mater. Trans. A 26 (1995), p 2207. [14] Y.M. Chen et al., Scripta Mater. 61 (2009) p. 693. [15] Emmanuelle A. Marquis et al., Mater. Today 13 (2010) p. 34. [16] F. Li et al., Scripta Mater. 63 (2010) p. 332. [17] David R. Diercks et al., Journal of the electrochemical society 161 (2014) p. F3039-F3045. [18] David R. Diercks et al., Journal of Materials Chemistry A 4 (2016) p 5167-5175. [19] B. P. Gorman, et al. Microscopy Today 16 (2008) p. 42-47.

Resume : Electrochemical Impedance Spectroscopy (EIS) is a widely applied tool in solid state ionics. It is used to analyze transport and adsorption processes as well as interfacial reactions for a large variety of electrochemical systems. Yet, there are elusive processes and intermediate reaction steps that cannot be identified just by analyzing the impedance of the system, defined as the transfer function between voltage and current. I will show how additional quantities can be probed in order to gain more information about processes and characteristics of the electrochemical system. Replacing voltage or current, i. e. excitation or response signal, in an EIS measurement by another physical quantity such as illumination or temperature leads to so-called generalized electrochemical impedance spectroscopy (GEIS) measurements, that open up a whole new field of measurement techniques just recently receiving interest in the materials community. Such measurements can be applied in situ and provide a general transfer function capable of being analyzed with the tools readily available for evaluating EIS data. In this talk I give an overview of GEIS measurements such as: intensity modulated photocurrent/-voltage spectroscopy (IMPS/IMVS), optical impedance spectroscopy (OIS) and electro-thermal impedance spectroscopy (ETIS). Practical examples it will be provided that demonstrate the new insights that can be gained with the aid of GEIS. An overview of experimental setups will also be provided. This work was supported by JSPS Core-to-Core Program, A. Advanced Research Networks.

Resume : Impedance spectroscopy is currently an indispensable tool in many subjects of solid state ionics and becoming even more popular. We researchers considered to have the expertise may have to admit that the techniques appear to be dead-ended. Many experimental data remain incompletely and unsatisfactorily explained. Physical modeling of AC behavior is done by the capacitor elements as well as the resistors. While the resistor components are unambiguously defined, ideal capacitors are rarely used. A good description of real experimental data using several constant phase elements (CPEs) should not be given too much significance, since the parameters of CPEs arbitrarily adjusted have no clear physical significance and the response of the respective CPEs extends over the entire frequency range. The procedure in estimating the effective capacitance parameters from the modeling employing CPEs is not absolutely justified nor unambiguous. It is suggested that the issues have been finally substantially clarified. Firstly, Havriliak-Negami capacitance function can describe the dispersive behavior with a reason such as relaxation, trapping, etc. and also define the capacitance magnitude for physical interpretation in terms of carrier or trap concentrations and geometry factors. Secondly, diffusion-involved electrochemical responses or percolating networks can be physically modeled by transmission-lines (TL) but CPEs are employed for shunt capacitance of TLs. In fact, many electrode polarizations can be satisfactorily described by TL with the ideal shunt capacitance in the presence of an ideal Warburg interfacial impedance. The capacitance effects are thus key to understand many impedance data. Often responses with different relaxations times can be systematically described by the superposition of capacitance effects, i.e. in parallel network, rather than the series network of the resistance effects. Importantly, these models have been recently implemented in a much used commercial fitting program and thus accessible for general experimentalists. Remarkably successful applications of the new impedance spectroscopy in the description of many different solid electrolytes, solid oxide fuel cells, photoelectrochemical cells, and batteries are presented

Resume : Thin film solid state batteries can play an important role in powering microdevices. Electrode materials for this application must hold high capacity, stability and be capable to discharge in a high rate. LiMn2O4 (LMO) has long been investigated as a cathode for Li-ion batteries, showing high specific charge capacity (148 mAhg?1). However, an excessive degradation rate has been reported, mainly due to Mn dissolution. Recent studies from our group have proven excellent ciclability of PLD deposited thin films of this material, showing an capacity retention of 99.996% per cycle after operating 3500 cycles at extremely high rates (348C). The understanding of the mechanisms leading to this excellent performances require of techniques capable to detect a change of the films properties during the (de-) intercalation process. Optical techniques, like Raman spectroscopy, are typically used for the in-situ study of cathode and anode materials. The use of spectroscopic ellipsometry for this purpose is much less common, despite being a powerful technique for thin film characterization. From optical constants it is possible to gain information about band gap structure and oxidation states. In this work, spectroscopic ellipsometry has been used for the first time for the in-situ study of LMO films during electrochemical cycling. The evolution of the absortion coefficient of the sample at different potentials gives insight in the lithium intercalation phenomena on this promising material.

Resume : Oxides such as ceria and praseodymium doped ceria exhibit large deviations from stoichiometry upon exposure to reducing environments and elevated temperatures. Thin films continue to gain attention, given interests in device miniaturization and related nanoscale effects. There is growing evidence that the nonstoichiometry of thin films might differ considerably from that of bulk counterparts due to inherent stresses induced by substrate constraints and/or high surface to volume effects. Only limited means exist, however, to accurately measure oxygen nonstoichiometry in films. In this work the nonstoichiometries of pulsed laser deposited CeO2-x and Pr0.1Ce0.9O2-x (PCO) thin films are investigated by resonant nanobalances at temperatures of up to 900 °C. The devices, consisting of high-temperature stable piezoelectric resonators, enable detection of mass changes on the order of nanograms by monitoring changes in resonant frequency. The oxygen activity in the films was controlled by varying the oxygen partial pressure from 10-20 to 10-12 bar and from 10-8 to 0.1 bar for CeO2 and PCO, respectively. The nonstoichiometry was found to range from x = 10-2 to 0.1 and x = 0.02 to 0.05 for CeO2 and PCO, respectively, in good agreement with previously reported thermogravimetry and chemical capacitance studies. Means for determining absolute values for x and issues that need close attention in achieving reliable data, e.g. temperature cross sensitivity, are discussed.

Resume : Graphitic carbon nitrides have emerged as an earth-abundant family of polymeric materials for various photo- and electro-catalytic applications. Herein, we report a 2D cyanamide-functionalized polyheptazine imide (NCN-PHI), which for the first time enables the synergistic coupling of two key functions of energy conversion within one single material: visible light harvesting and electrochemical energy storage. We reveal the underlying mechanism of this ?solar battery? material by photo-electrochemical measurements in aqueous electrolytes, showing that the charge storage in NCN-PHI is based on the photoreduction of the carbon nitride backbone while charge compensation is realized by the adsorption of alkali metal ions within the NCN-PHI layers and at the solution interface. The photoreduced carbon nitride can thus be described as a battery anode operating as a pseudocapacitor, which can store light-induced charge in the form of long-lived, ?trapped? electrons for hours. Importantly, the potential window of this process is not limited by the water reduction reaction due to the high intrinsic overpotential of this carbon nitride for the hydrogen evolution reaction. Owing to these properties, the complexity of solar batteries is significantly reduced and higher cell voltages for aqueous batteries are possibly enabled. Thus, the feasibility of light-induced electrical energy storage and release on demand by a one-component light-charged battery anode is demonstrated, that provides a sustainable, earth abundant solution to overcome the intermittency of solar irradiation and other renewable electrical energy sources at a time. Further information can be found in: ?Dark photocatalysis: Storage of solar energy in carbon nitride for time-delayed hydrogen generation?, V.W.-h. Lau et al.,, Angew. Chem. Int. Ed. 2017, 56, 510?514 and ?Toward an Aqueous Solar Battery: Direct Electrochemical Storage of Solar Energy in Carbon Nitrides?, F. Podjaski et al., Adv. Mater. 2018, 1705477.

Resume : The electrical conversion and storage of solar energy is a crucial target for assuring the world energy supply in the long term. A critical parameter for the implementation of standard high-efficiency photovoltaic absorber materials for photoelectrochemical water splitting is its proper protection from chemical corrosion while remaining transparent and highly conductive. Atomic layer deposited (ALD) TiO2 layers fulfill material requirements while conformally protecting the underlying photoabsorber. Nanoscale conductivity of ALD TiO2 protective layers on silicon-based photocathodes has been analyzed, proving that the conduction path is through the columnar crystalline structure of TiO2. Because of the sluggish kinetics associated to the water oxidation reaction and of inherent limitations in the H2 economy, the possibility of storing energy to other kind of redox pairs has recently attracted more attention, giving rise to the so-called solar-powered electrochemical energy storage (SPEES), The ability of protected crystalline silicon to photoassist the V3+/V2+ cathodic reaction under simulated solar irradiation, combined with the effect of bismuth have led to important electrochemical improvements. High reversibility of the V3+/V2+ redox pair, and improvement in the electrokinetics were attained thanks to the addition of bismuth. In fact, Bi0 deposition has shown to slightly decrease the photocurrent, but the significant enhancement in the charge transfer, reflected in the overall electrochemical performance clearly justifies its use as additive in a photoassisted system for maximizing the efficiency of solar charge to battery.

Resume : Water splitting provides a clean and renewable way to produce high-purity hydrogen, but its practical application has been limited by the slow kinetics and poor stability of the electrocatalysts. Here we report a facile preparation of Pt-Co open hollow clusters embedded in carbon nanoflake arrays aligned on flexible carbon cloth (Pt-Co/C NAs, 2.5 wt% Pt), which display excellent electrocatalytic activity and ultra-long durability for both hydrogen and oxygen evolution in alkaline media. The high performance arises from the synergistic effect of the unique open hollow Pt-Co nanostructure embedded in the conductive carbon nanoflake arrays. The material can be utilized directly as a bifunctional catalyst for overall alkaline water splitting. It outperforms noble-metal-based materials in terms of much lower operation voltage (1.54 V at a current density of 10 mA cm-2) and higher stability (no degradation at constant current or voltage up to 120 h), representing a highly promising electrode for electrochemical energy conversion.

Resume : For large scale storage of excess electrical energy CO2 electrolysis may become very important, since it offers a method of sustainable CO production, which can serve as a basis for synthesis of regenerative carbon-based fuels. CO2 reduction in solid oxide electrolysis cells (SOECs) is particularly promising, since their high operating temperature facilitates both thermodynamics and reaction kinetics. In this work, the evolution of surface chemistry of (La,Sr)FeO3-? and (La,Sr)CrO3-? based perovskite-type electrodes was studied operando by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) during electrochemical CO2 reduction at SOEC operating temperatures. In these experiments a carbonate intermediate was identified, which only forms upon cathodic polarization. In contrast to previously studied high temperature water splitting, the CO2 electro-reduction reaction was not significantly affected by exsolved metallic particles decorating the electrode surface. Together with an analysis of polarization-induced XPS peak shifts this behavior identifies the oxide rather than the metal particles as the adsorption sites of the carbonate. Based on these observations as well as the influence of the defect chemistry of the oxide electrode on the carbonate coverage, a reaction mechanism for high temperature CO2 reduction on perovskite-type oxides is discussed.

Resume : Water splitting is a rising technology with the potential to enable a future hydrogen economy. Thermochemical redox reactions are one established method to produce hydrogen with a minimal carbon footprint. The current state-of-the-art redox active material, ceria, boasts fast kinetics and high cyclability. Issues however arise as high reaction temperatures are necessary. Consequently, alternative oxygen exchanging materials are being actively explored. Strontium cobalt oxides doped with antimony, molybdenum and niobium are promising materials for low temperature thermochemical water splitting due to their mixed ionic electronic conductivity. Additionally, thanks to toptactic reversible redox cycling they exhibit large oxygen storage capabilities at intermediate temperatures (480-800 °C).1-3 Thermogravimetric analysis using alternating inert and oxidising environments reveal the 5% molybdenum-doped powders to have the most encouraging reaction kinetics and expected hydrogen production up to 450 umol/g at 800 °C. Future observations by gas chromatography aim to elucidate the precise rates and hydrogen production quantities allowing a direct comparison to be made with current published materials. 1. A. Aguadero et al., Chem. Mater., 2010, 22, 789-798 2. A. Aguadero et al., Chem. Mater., 2012, 24, 2655-2663 3. V. Cascos et al., Int. J. Hy. En., 2014, 39, 14349-14354

Resume : Efficient approaches for the utilisation and management of effluent emission of CO2 are highly important subjects. Reducing CO2 emissions and converting it into useful fuels by renewable energy has been an attractive approach, using solid oxide electrolysis cells (SOECs) as a promising energy storage device. This allows effectively mitigating the increase of CO2 in the atmosphere and even producing useful fuels (e.g. H2/CO syngas and hydrocarbon source). Previously Ni-based cermet materials are usually used as fuel electrodes for SOECs. High activity and low degradation rate of the conventional cathodes is essential for the application of high-temperature electrolyser. Hence, to improve the stability, utilisation of perovskite oxides as fuel electrodes recently has been highly suggested instead of metallic-based electrodes. However, there are some critical drawbacks in perovskite materials used for the cathode in SOEC. Insufficient current density or catalytic activity limits the operation in a low- and intermediate temperature. For example, in our previous case of La(Sr)Fe(Mn)O3 cathode, an average current density of ~0.65 A/cm2 was achieved at ~1.6 V and 800°C. In addition, significant A-site segregation (SrO) is generally formed on the surface at an elevated temperature, likely leading to a certain chemical reaction (SrCO3), and consequently degradation when particularly operating in a CO2 reduced atmosphere. Therefore, we proposed to use spinel oxides, a general formula AB2O4, which are composed of two transition metals. Spinel oxides have been used in various catalytic applications (for example, decomposition of gaseous pollutants and water gas shift reaction). This type of material is expected to provide a higher current density of electrolysis and possess a mixed termination of transition metals as active roles to facilitate the reduction of CO2 and H2O. In this study, we investigate a number of spinel oxides as cathodes applied in the electrolysis of CO2 and steam co-electrolysis using LSGM as the electrolyte. Galvanostatic measurements, electrochemical impedance spectroscopy and microstructural analysis have been conducted to investigate the cell performance. In addition, the formation of the syngas CO/H2 in operation was measured by gas chromatography. It was found that one of spinel oxide, CuFe2O4, can perform promising current density values of ~1.2 A/cm2 and ~2.0 A/cm2 have been achieved in CO2/H2O and H2O electrolysis at ~1.6 V and 800°C. Also, this material shows excellent conversion efficiency of CO H2 or H2, approximately over 95% achieved. Therefore, spinel oxide may be a potential type of cathode candidates for the application of CO2/H2O and H2O electrolyser.

Resume : High value-added synthetic gas can be produced through co-electrolysis of carbon dioxide (CO2) and water vapor (H2O) using high-temperature solid oxide cells (SOCs). However, conventional Ni-catalysts based SOC shows relatively low CO2 conversion efficiency and poor selectivity of carbon monoxide. Hence, in this study, a useful model experiment was designed to understand the exact reaction mechanism of CO2 conversion during co-electrolysis, thereby we can select the optimum catalyst for co-electrolysis cells. Thin-film type heterogeneous alloy catalysts were introduced to more clearly compare the activity of alloy catalyst with respect to its composition and effective surface area. In order to precisely control the composition and quantify the effective surface area of catalysts, thin-film and in-situ nano-alloying techniques were employed. In-situ XPS and NEXAFS analysis were carried out to investigate the composition/structural change of catalyst surface and identify the intermediate product form of catalytic reaction in real operating environment. Some computational work was also carried out to verify the reaction mechanism. In this presentation, from the fundamental understanding of CO2 conversion reaction mechanism, some candidate catalysts that can improve the CO2 conversion efficiency and the selectivity of carbon monoxide will be proposed.

Resume : Next generation of energy storage and sensors may largely benefit from fast Li+ ceramic electrolyte conductors to allow for safe and efficient batteries and real-time monitoring anthropogenic CO2. Recently, Li-solid state conductors based on Li-garnet structures received attention due to their fast transfer properties and safe operation over a wide temperature range. Through this presentation basic theory and history of Li-garnets will first be introduced and critically reflected towards new device opportunities demonstrating that these electrolytes may be the start of an era to not only store energy or sense the environment but also to emulate data and information based on simple electrochemistry device architecture twists. In the first part we focus on the fundamental investigation of the electro-chemo-mechanic characteristics and design of disordered to crystallizing Li-garnet structure types and their description. Understanding the fundamental transport in solid state and asking the provokative question: how do Li-amorphous to crystalline structures conduct? As well, as how can we alter their charge-and mass transport properties for solid electrolytes and towards electrodes is discussed. Here, we firstly present new Li-garnet battery architectures for which we discuss lithium titanate and antimony electrodes in their making, electrochemistry and assembly to full battery architectures1-4. Secondly, new insights on degree of glassy to crystalline Li-garnet thin films are presented based on model experiments of the structure types. Here, the thermodynamic stability range of maximum Li-conduction, phase, nucleation and growth of nanostructure is discussed using high resolution TEM studies, near order Raman investigations on the Li-bands and electrochemical transport measurements. The insights provide novel aspects of material structure designs for both the Li-garnet structures (bulk to films) and their interfaces to electrodes, which we either functionalize to store energy for next generation solid state batteries or ... make new applications such as Li-operated CO2 sensor tracker chips. As a final part we review in a more holistic picture how one can use such materials and change the electrochemistry from energy storage, chemical sensing to data emulation for which we see prospect for electric vehicles, the Internet of Things or hardware in artificial intelligence.

Resume : Solid electrolytes with Li-ion conductivity higher than 1 mS/cm are required for the development of high capacity solid-state Li-ion batteries. In the past decade, several studies were done on the improvement of ion conductivity in composite materials by employing interface enhanced ion conduction at inorganic oxide surfaces. Also, composites of oxide nanoparticles or mesoporous oxide microparticles mixed with ILE have been proposed. However, so far the ionic conductivity was always lower than that of the original ILE due to the interrupted ionic paths by percolation from particle to particle. Enhancement of the Li-ion conductivity is shown for solid nanocomposite electrolytes (SCE) based on a mesoporous silica monolith functionalized with an ionic-liquid electrolyte (ILE). The ionic conductivity of the SCE pellet exceeded that of the pure ILE liquid with over 100%, well surpassing the 1mS/cm threshold. A mechanism for enhanced ion conduction through a surface adsorbed mesophase layer is proposed.

Resume : Understanding and controlling lithiation reaction pathways in Si-based anodes, such as nucleation and evolution of Li-Si phases, defect interactions, and transport of Li ions, are crucial for developing high-performance Li-ion batteries. With a theoretical capacity of ~4200 mAhg-1, which is more than 10 times greater than that of graphite, the practical use of Si anodes is, however, hampered by capacity fading and large volume changes that occur during cycling. Deeper insights into the reaction mechanisms at the atomic level are vitally needed to address this problem. In this work, we report on recent progress in studies of the lithiation of model thin film Si membranes with a low-energy focused Li-ion beam (LiFIB). The scanning LiFIB enables a Li probe size of a few tens of nm at energies ranging from 500 eV to 5 keV and beam currents up to 15 pA, allowing one to inject Li cations directly into the material with a nanoscale precision. This approach avoids electrochemical processing in electrolytes and the formation of a solid-electrolyte interface. We investigated microstructural evolution of the membranes and defects induced by Li-Si interactions vs. ion dose and characterized surface electrostatic potentials and lateral distributions of lithium in the implanted regions using spatially-correlated Kelvin probe force microscopy, HRTEM, electron diffraction, and STEM-EELS. Our findings indicate that nanoscale processes that occur at early lithiation stages involve a series of solid state transformations, including clustering of interstitials in tetragonal sites of the c-Si lattice, creation of interstitial-rich extended defects, and substantial amorphization of the Si matrix followed by the formation of various LixSi phases.

Resume : Herein, we report, for the first time, the preparation and the characterization of an interpenetrated polymer network electrolyte (IPNE) in a thin film lithium µ-batteries (µLIBs). The IPNE was prepared by thermal free radical polymerization of methacrylate oligomers in the presence of 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide (P14FSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) 1 The study was conducted by varying the composition of the cross-linked electrolyte (e.g. the ratio of RTIL/oligomers and LiTFSI/RTIL, the rate of cross-linking) in order to achieve an optimized composition allowing a compromise between mechanical properties, liquid confinement inside the polymer network and electrochemical performances of the quasi-solid IPNE. Lithium transference number and ionic conductivity were determined as function of the electrolyte composition and Nuclear Magnetic Resonance (NMR) spectroscopy with Pulsed Field Gradients (PFG) was used in order to measure the self-diffusion coefficients in the electrolyte. Furthermore, a thin film Lithium µ-battery was successfully constructed and cycled. The µ-battery was consisting of a stack of a thin layers of active materials (lithium anode, LCO cathode and IPNE) where the IPNE plays a role of both electrolyte and separator. The thin lithium anode (5 µm thick) was directly grown on the IPNE (5 to 10 µm thick films) by metal thermal evaporation technique leading to a compact and stable lithium/polymer electrolyte assembly which was further added to a thin LCO cathode to get the full µ-battery. After assembling, the µ-battery showed an open circuit voltage around 3 V and was cycled at different speed showing excellent capacity retention even at high speed (1C) and very promising stability (over 100 cycles). References: [1] F. Ghamouss, V. Chaudoy. E. Luais, F. Pierre, F. Tran-Van, « Microbatterie au lithium et procédé de fabrication », PCT/Fr2017/053086. Patent.

Resume : All solid state Li metal batteries are the most promising candidate due to their expected high energy density for next electrical vehicles (EV-HEV) generation. Among possible candidate materials for solid electrolyte, the oxide ceramic super lithium ion conductors, garnet-type Li7La3Zr2O12 (LLZO) has recently attracted much attention because of its relatively high ionic conductivity at room temperature (>10-4 S cm?1), negligible electronic conductivity and absence of harmful decomposition products upon contact with atmospheric moisture. Anyway, processing LLZO in pellets by sintering, results in brittle and more or less porous electrolytes, which often display poor interfacial contact with Li metal electrodes. Moreover, there are some reports of lithium dendrite growth and instability towards the cathode material - especially while processing of the electrode at high temperature - referred to cells assembled with this electrolyte family [1,2]. To circumvent these problems, recent efforts have been dedicated to the formulation of composite hybrid polymer electrolytes (CPEs), where the ceramic material is embedded in a polymeric matrix. As compared to the pristine components, CPEs are stiff while preserving flexibility, are easily processed, and can be conceived to attain improved ionic conductivity and interfacial contact with the electrodes [3]. In this work, a polymer based matrix containing poly(ethylene oxide) (PEO), lithium bis (trifluoromethylsulphonyl)imide (LiTFSI), tetra(ethylene glycol dimethyl ether) (G4) and a photoinitiator was added with LLZO particles, thoroughly mixed, formed into a film and cross-linked under UV radiation to obtain a composite hybrid electrolyte [4]. This easy procedure allows obtaining self-standing CPEs with desirable properties of flexibility, shape retention upon thermal stress, improved interfacial contact with the electrodes and ionic conductivity suitable for practical application. Lab-scale all solid lithium metal cells assembled with the CPEs and lithium iron phosphate (LFP) cathodes demonstrated specific capacities up to 125 mAh g-1 at 1C rate and could work for hundreds of cycles at ambient temperature. [1] B. Liu, Y. Gong, K. Fu, X. Han, Y. Yao, G. Pastel, C. Yang, H. Xie, E.D. Wachsman, and L. Hu, ACS Appl. Mater. Interfaces 9 (2017) 18809-18815. [2] H. Duan, H. Zheng, Y. Zhou, B. Xu, and H. Liu, Solid State Ionics (2017) in press. [3] C. K. Chan, T. Yang, and J.M. Weller, Electrochim. Acta 253 (2017) 268?280. [4] L. Porcarelli, C. Gerbaldi, F. Bella, and Jijeesh R. Nair, Sci. Rep. 6 (2016) 19892.

Resume : The demand of portable energy has grown during last 25 years, due to the spread of electronic personal devices and it will increase to boost the turn toward an oil-free mobility.[1] Such revolution based on Li-ion cell, has to face many constraints, i.e. the costs of raw materials and the security issues due to the use of a flammable electrolyte.[2] Na-based solid-state batteries could tackle these hurdles. They use the more abundant sodium as charge carrier and they feature a safer, solid material as electrolyte. Herein, the novel Na4(CB11H12)2(B12H12) was synthetized by solid-state ball-milling. It shows high Na+ conductivity, 1 mS cm-1 at 20°C, which increases to 10 mS cm-1 at 100 °C (Ea=136 meV). CV performed with a specific setup for solid electrolytes[3] revealed an excellent electrochemical stability, up to 4.1 V vs. Na+/Na. Preliminary tests on the electrolyte?s stability toward metallic Na in symmetric cells showed a limited electrolyte-electrode compatibility, (increase of the internal cell resistance) as already observed elsewhere.[4] Replacing Na by Na-Sn alloy a stable Na+ shuttling has been achieved, with low polarization over one month of cycling. In situ monitoring of the internal cell resistance by EIS confirmed the good stability of the electrolyte-electrode interface. [1] Zeier et al Nat Ener 1 (2016) 16141 [2] Sun et al Nano Ener 33 (2017) 363 [3] Tian et al Energy Environ Sci 10 (2017) 1150 [4] Iermakova et al J Electrochem Soc 162 (2015) A7060

Resume : Sodium-ion batteries for large-scale energy storage have recently attracted attention due to larger reserves of raw materials and possibly lower cost in comparison with lithium-ion cells. Batteries following an all-solid-state approach promise higher charging rates, less flammability and the minimization of hazardous material but challenge scientists with high interface resistivities. Here we report on the connection between the interface resistivity and battery performance in sodium all-solid-state batteries with Na-super ionic conductor Na3.3Sc0.3Zr1.7Si2PO12 (NASICON) and ß??-alumina solid state electrolytes. Experimental batteries were produced with Pulsed Laser deposited (PLD) NaxCoO2 films on solid electrolyte substrates. NaxCoO2/Nasicon/Na and NaxCoO2/ß??-alumina/Na Swagelok-type cells were cycled at room temperature with intermediate electrochemical impedance measurements. Interface resistances between the cathode, the solid electrolyte and the sodium anode were identified and monitored with increasing cycling number. Optimized all-solid-state batteries were cycled at rates between C/5 and 2C in a voltage range of 2.0 and 4.2 V. They exhibit interface resistivity?s of 600 Ohm cm² and specific capacities of 125 mAh/g with a capacity fading of only 10% over 1000 cycles.

Resume : Redox-based resistive switching random access memory (ReRAM) is considered as promising future low energy non-volatile storage device with high-speed data access and high reliability. Valence-change-memory (VCM) cells typically require an electroforming step to create conductive paths in the mixed ionic-electronic conducting (MIEC) oxide by means of local extraction of oxygen. For the resulting filamentary-type bipolar resistive switching behavior oxygen vacancy drift/diffusion processes play a major role. However, with decreasing device dimensions the effect of oxygen exchange reactions between the MIEC switching layer and the electrodes becomes more pronounced. Recently, the importance of oxygen exchange reactions at the interface of Ta2O5 and the chemically reactive electrode has been demonstrated. Additionally, a coexistence of switching events of opposite polarity has recently been reported for cells built of heteroepitaxial SrTiO3 films as well as for crossbar structures made of nano-crystalline TiO2 layers. Ultra-high density integration of massively connected ReRAM cells into three-dimensional blocks for future beyond-von Neumann memory architectures requires a deeper knowledge on the switching behavior of nano-scaled devices. This includes a deeper understanding of the competition between oxygen ion drift/diffusion vs. oxygen exchange reactions. The presentation will address these questions with a focus on Pt/3-5 nm TiO2/Ti/Pt nano-crossbar devices which show a coexistence of two switching polarities, in detail, the counter-eightwise (c8w) and the eightwise (8w) behavior. For the studied cells, the two switching modes share one state, this is that the c8w-HRS equals the 8w-LRS*.

Resume : Resistive switching based on transition metal oxide memristive devices is suspected to be caused by the electric field driven motion and internal redistribution of oxygen vacancies. Deriving the detailed mechanistic picture of the switching process is complicated, however, by the frequently observed influence of the surrounding atmosphere. Although an increasing number of models used to explain atmospheric influences are based on the release and reincorporation of oxygen species, the experimental evidence for these exchange processes is scarce. To investigate the role of oxygen during resistive switching in greater detail, we use isotope labeling experiments in N2/H218O tracer gas atmosphere combined with time-of-flight secondary ion mass spectrometry. We explicitly demonstrate that oxygen incorporation processes take place in resistive switching SrTiO3-based memristive devices. Specifically, we observe that during the RESET operation, voltage driven oxygen incorporation occurs predominantly by water present in the atmosphere. These findings clarify in detail the exchange of oxygen between SrTiO3 and the ambient atmosphere during device operation and resolve the role of humidity for the oxidation process during the RESET operation.

Resume : This work presents the design of memristive heterostructures using LaMnO3+? (LMO) as ?sandwiched? switching material between the top and bottom electrodes. A number of different strategies were explored to integrate these manganite films on silicon-based devices, overcoming the challenge of the high temperatures required for their deposition. LMO thin films were prepared by pulsed injection MOCVD and were fully characterized using a combination of microscopic, spectroscopic and physical techniques. A rhombohedral phase is obtained for films treated under O2, pointing out to higher oxygen concentration (3+?); whereas films treated under Ar showed an orthorhombic phase, linked to a lower oxygen content (higher VO.. concentration). The resistivity values obtained have been related to the structural, compositional and electronic properties of the LMO films. The resistive switching (RS) response for different LMO-based devices was optimized as a function of the nature of the electrodes, the LMO microstructure, the forming step and the set/reset voltages applied. Bipolar RS with different memory windows was attained by tuning the voltage and the current compliance. The nature of the switching mechanism will also be discussed (filamentary vs interfacial). The RS results obtained are very promising, showing a large resistance window for operation (up to 3 orders of magnitude) and using low set/reset voltages for the three different top metal electrode configurations tested.

Resume : The human brain processes large amounts of information in parallel at low energy cost. The energy-efficiency, cognitive ability, and versatility of this integrated memory and logic system have inspired the field of neuromorphic computing. Synapses are one of the most vital components of neuromorphic networks. They act as connections between neurons. Voltage pulses that are applied to a synapse modify the synaptic weight through long-term potentiation (LTP) and short-term plasticity (STP), enabling memory and cognitive activities. Memristors with gradually modifying conductivity levels can mimic the behavior of biological synapses. Low energy consumption, fast operation and small dimensions are essential requirements for the integration of memristors into neural networks. In recent years, several types of memristive devices have emerged, including devices that are based on ferroelectric polarization switching, phase changes, magnetization dynamics, and ion migration. In our previous work, we have shown that oxide tunnel junctions with ionic interfaces are able to show large resistive switching between on and off states due to electric-field controlled migration of oxygen vacancies. In this work, we demonstrate that the resistance of junctions with a La2/3Sr1/3MnO3 bottom electrode, a Au top electrode, and a thin SrTiO3 tunnel barrier can be continuously set to any intermediate states by controlled migration of oxygen vacancies under varying voltage pulses. This memristive behavior together with synaptic features like long-term potentiation and depression makes them attractive for applications as electronic synapse in neural networks.

Resume : Resistive switching memory (ReRAM) is a prominent candidate for next generation non-volatile storage devices. Redox-type valence change memories (VCM) based on HfO2 and Ta2O5 switching layers typically show a counter-eightwise (c8w) polarity of the switching loop which is clearly associated with filamentary-type switching. Interestingly for epitaxial grown SrTiO3 based devices also switching loops of eightwise (8w) polarity have been reported. Recently, 8w switching hysteresis has also been reported for cells based on polycrystalline TiO2 thin films. Here, we report on TiO2 based nano-crossbar cells of Pt/(Al2O3)/TiO2/Ti/Pt with a Al2O3 layer of 0 to 3 nm and a TiO2 layer of 3 to 6 nm. To achieve conformal growth on the 100 nm wide Pt bottom electrode lines the oxide layers were deposited by thermal atomic layer deposition. The 10 nm Ti oxygen exchange layer and the Pt layer were grown by e-beam evaporation. Cells from pure TiO2 as well as bilayer cells with up to 2 nm of Al2O3 reveal a coexistence of the two switching polarities (c8w and 8w) in the same device. The 8w bipolar resistance switching mode can be operated in the current range below 100 µA and offers the possibility of programming stable multilevel high resistance states. In order to understand the switching behavior in these devices, different high resistance states of the 8w switching mode were carefully analyzed with respect to their current dependence on temperature and electric field. The corresponding I(V, T) behaviors were successfully characterized by application of the Simmons? formula for tunneling through an asymmetric barrier. With the simulation parameters, a qualitative understanding of the multilevel switching behavior in both mono- and bilayer cells is established.

Resume : Implementation of a memristor suitable for computing and data storing is a one of rising recent research trends. Many applications are to be implemented within a one- and a multi-bit memristors. It can be used to increase the information capacity of RAM elements as well as to be used for neuromorphic computational systems that can bring the AI to a completely new level. Although it is simple enough to implement the memristor using macrostructures, it is not applicable for the computing purposes. Research on thin metals oxide films shows the applicability of such an object for the objective ? creating the memristor with desirable characteristics. It is tended to connect the memristive switch with the filament formation that occurs when a current pulse passes over a dielectric. The aim of the work is obtaining a model of dynamic memristor switching possessing by analysis of charge transport in high-k affected by the presence of defects and heat release. A continuum filament growth model is formulated. The model is the boundary value problem, which includes a nonstationary heat conduction equation with a nonlinear Joule heat source, Poisson equation, and Shockley-Read-Hall equations considering strong electron-phonon interactions in trap ionization and charge transport processes. The results of computer simulations of the model are current-voltage characteristics of a memristor element. The work was supported by the Russian Science Foundation, grant #16-19-00002.

Resume : Mixed ionic and electronic conductors can change their chemical composition through mass exchange with the external environment, both chemically and electrochemically. Examples include oxygen-insertion compounds such as ceria oxide, and lithium-insertion compounds such as lithium cobalt oxide. The insertion or removal of mass such as oxygen or lithium causes an expansion or a contraction of the lattice, resulting in a chemo-mechanical coupling. In this talk I will present three special cases of such coupling. The first case is biaxially-strained, dense thin film of cerium oxide. The tetragonal distortion of the nominally cubic crystal gives rise to splitting of the oxygen redox levels, leading to a non-monotonic dependence of oxygen concentration on strain. The second case is porous agglomerate of lithium transition metal layered oxide, which exhibits significant compositional heterogeneity at equilibrium, again due to chemo-mechanical coupling. Finally, I will discuss the importance of chemo-mechanics at interfaces such as grain boundaries.

Resume : The oxygen exchange reaction on mixed ionic electronic conducting (MIEC) oxides is highly important for solid oxide fuel cells, sensors or oxygen permeation membranes. To characterize the kinetics of surface oxygen exchange, isotope exchange depth profiling (IEDP) and electrochemical impedance spectroscopy (EIS) are usually regarded as complementary tools, simply assuming the electrical (kq) and tracer (k*) surface exchange coefficients to be identical. Only very few studies directly compared kq and k* of solid?gas interfaces under identical conditions. In this work it is shown that kq and k* may strongly differ for one material and different humidification, but also between different MIEC materials. In-situ EIS with oxygen exchange experiments were performed on La0.8Sr0.2MnO3-?, La0.6Sr0.4CoO3-?, La0.5Sr0.5Co0.2Fe0.8O3-?, La0.6Sr0.4FeO3-? and SrTi0.3Fe0.7O3-? thin films. Experiments were performed in usual isotope exchange conditions (18O2), in dehumidified 18O2 isotope (by a molecular sieve), humid oxidizing (18O tracered O2 and H2O) and humid reducing (H2 tracer H2O) atmospheres. In dried isotope gas kq and k* were rather similar (k*/kq=1.5), whereas in humid atmospheres the difference between k* and kq becomes tremendous (k*/kq=1000) for some materials. The reason behind this is a fast water adsorption and dissociation on surface oxygen vacancies, by forming surface hydroxyl groups. Experimentally determined k* and kq values are discussed in terms of electrochemically relevant oxygen exchange and temperature dependence for five different MIECs.

Resume : The reversible operation of Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC) for the interconversion of electrical and chemical energy requires a good electro-catalytic activity and the long-term stability of the ceramic air electrode with the surrounding atmosphere. In particular, the interaction of oxygen-bearing molecules in the feed gas with the electrode surface is a critical process to understand. This work investigates the influence of water vapour (up to 100 mbar) and carbon dioxide (up to 5 mbar) on the evolution of the surface chemistry and on the changes to the oxygen transport kinetics of LSCF6428 as a model air-electrode. A ?back exchange? protocol [1,2] and H218O labelling are used to probe the oxygen transport kinetics under 0.20 bar of oxygen. A systematic increase of the surface exchange kinetics is observed in the presence of steam or CO2. Unexpectedly, the diffusion kinetics are also affected. The evolution of the surface with time and the exposure to different atmospheres is followed, in particular by the mean of Low Energy Ion Scattering (LEIS). [1] S.J. Cooper, M. Niania, F. Hoffmann, J.A. Kilner, Phys. Chem. Chem. Phys. (2017). [2] H. Téllez, J. Druce, S.J. Cooper, J.A. Kilner, Sci. & Tech. of Adv. Mat. (2017). This work was supported by JSPS KAKENHI Grant Number 16K18236. This work was supported by the WPI program. This work was supported by JSPS Core-to-Core Program, A. Advanced Research Networks.

Resume : Pt/YSZ is one of the best studied model systems for oxygen reduction in solid state electrochemistry with a long history of research and especially at high temperatures it is the prototype of a triple phase boundary (TPB) active electrode. However, the exact reaction mechanism of oxygen reduction on Pt/YSZ in general and its rate limiting elementary step in particular are still not completely understood. To shed further light on the oxygen exchange kinetics of this system the polarization resistance of micro-patterned Pt thin film electrodes on YSZ (111) single crystals was studied by means of impedance spectroscopy at low oxygen partial pressures between 0.1 and 0.01 mbar. Under these conditions a hysteretic behavior of the polarization resistance could be found for temperature sweeps between 500 and 850 °C. The associated step-like increase/decrease of the polarization resistance was further analyzed by variation of the electrode geometry to identify potential changes in the electrochemically active region. Moreover, possible reaction mechanisms explaining this yet unknown behavior of Pt(O2)/YSZ are discussed.

Resume : La1-xSrxMnO3 (LSM) was one of the first perovskites employed as SOFC cathode and is still used in composites. We analyzed oxygen adsorption, dissociation and migration on the (001) MnO2-terminated surface [1]. In pure LaMnO3, the MnO2 (001) termination was found to be the energetically most stable, however with an increase of Sr doping, the (La,Sr)O termination becomes more favorable [2]. In this talk, we compare results of first principles calculations on the elementary steps (oxygen vacancy formation, O2 molecule and O atom adsorption) of oxygen reduction on the polar (La,Sr)O and MnO2 (001) terminations. Slab calculations were performed using VASP with GGA functionals. In contrast to the MnO2 termination, the vacancy formation energy on (La,Sr)O is larger, strongly reducing the surface vacancy concentration. Our approach distinguishes two effects - different surface terminations and slab cation stoichiometry (ratio of (La,Sr) ions to Mn affecting the average Mn oxidation state). The equilibrium oxygen adsorbate concentration was found to be two orders of magnitude larger for (La,Sr)O, but on the other hand, the surface oxygen vacancy concentration is smaller by nearly six orders of magnitude. Therefore, the oxygen reduction rate on (La,Sr)O is expected to be significantly lower than on MnO2. [1] Y.A. Mastrikov, R. Merkle, E. Heifets, E. A. Kotomin, J. Maier, J.Phys.Chem.C 114, 3017 (2010). [2] S. Piskunov, E. Heifets, T. Jacob, E.A. Kotomin, E. Spohr, Phys. Rev.B 78, 121406 (2008)

Resume : In heteroepitaxial thin film growth the mismatch between film and substrate cell structures causes the films to start growing with a certain strain until a certain critical thickness is achieved. Above this thickness the strain energy starts to be gradually released by different possible mechanisms. One of the most common mechanisms for strain relaxation is the formation of misfit dislocations (MDs). In perovskite oxides the most common dislocations are of pure edge character following characteristic crystallographic directions, depending on the film orientation and substrate cut. The dislocations start forming at the film surface and diffuse across the film thickness until they reach the film-substrate interface. The dislocation core is intrinsically a discontinuity in the material structure and therefore it can show different material properties at a local scale. Concomitantly, the film regions surrounding one single MD core are submitted to a particularly strong strain field, compressive or tensile at opposite regions of the MD core. This strain field may as well substantially modify the equilibrium structure giving rise to differences in the material functionality around these local dislocated regions. Under particular conditions the dislocation strain fields of adjacent MDs interact generating a self-arrangement and forming organised arrays with a few nanometres scale spacing. These region can be, therefore, considered as a nanostructure embedded at the interfacial region between a relaxed film and the substrate, and pave the way to interesting application in nanodevices, as well of facilitating the fundamental study of the peculiar functionalities of these 1D objects. In this study we present different cases of MDs arrangement during epitaxial growth, particularly in compressively strained LaSrMnO3 grown on LaAlO3(100) substrates. The dislocation distribution is readily analysed by X-ray diffraction and AFM [1,2]. The structure of the core and surrounding area of the MDs is analysed by HRTEM, as well as its chemical and electronic configuration at atomic-column resolution by means of combined EDS and EELS analysis.[3] These studies reveal a complex interplay between local anionic and cationic composition as well as changes in the transition metal oxidation state which depend on the compressive or tensile region around the MD core. The mechanisms underlying the changes in the local structure and composition in the dislocated regions result from a combination of elastic and electrostatic energy degrees of freedom and the sign and magnitude of the film-substrate mismatch. [1] J. Santiso et al., ACS Appl Mater Interfaces. 8 (2016)16823-16832 [2] F. Sandiumenge, Adv. Mater. Interfaces 3 (2016) 1600106. [3] N. Bagués et al., Adv. Funct. Mater. (2017) 1704437. doi: 10.1002/adfm.201704437

Resume : Pr substituted CeO2 (PCO) is an excellent model mixed ionic-electronic conductor (MIEC) for fundamental studies and has potential applications in intermediate temperature electrochemical devices. In high pO2 conditions, vacancy formation is accompanied by the reduction of Pr4 to Pr3 and the material displays MIEC behaviour via oxygen vacancy migration and small polaron hopping between the valence-active cations. PCO has been extensively studied, and the defect chemistry, chemical expansion, and transport properties are well described in the bulk material. This makes it an excellent choice for studying the interplay of strain, space-charge, and electro-chemo-mechanical coupling effects at heterogeneous interfaces, including their impact on transport properties. We have fabricated multilayer films of alternating Pr0.1Ce0.9O2-d and SrTiO3 (STO) layers using pulsed laser deposition. The nanostructures have been characterised in detail using X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy combined with electron energy loss spectroscopy. The conductivity of the layers shows a dramatic weakening of the pO2 dependence as the density of the interfaces is increased, which is consistent with a lowering of the enthalpy for Pr reduction. This study represents an excellent example of the significant potential to tailor the ionic and electronic transport at oxide interfaces

Resume : Oxide heterointerfaces can harbor electronic systems with a variety of remarkable properties, like superconductivity, magnetoresistance or tunable metal?insulator transitions. Since the discovery that a two-dimensional electron gas (2DEG) can be formed at the LaAlO3?SrTiO3 interface, SrTiO3-based interfaces have been in focus of research. For many SrTiO3-based interfaces, such as amorphous LaAlO3?SrTiO3, gamma-Al2O3?SrTiO3, or irradiated SrTiO3, the electron density is determined by oxygen vacancies, which accumulate at the interface and act as donor dopants. In recent experiments, it has been shown that the spatial distribution of oxygen vacancies can be controlled by annealing and thereby the electron density can be tuned. To support further experimental efforts, we describe the redistribution of oxygen vacancies and the corresponding changes in electron density during annealing with a time-dependent drift?diffusion model. This model is based on space-charge theory: the lowered chemical potential of oxygen vacancies at surfaces and interfaces is considered as thermodynamical driving force for the oxygen vacancy redistribution. We show that oxygen vacancies form a depletion layer close to the interface, which implies a spatial separation of oxygen vacancies (donors) and electrons. The timescale of this redistribution strongly depends on the ambient conditions, e. g. it ranges from weeks at 300 K to seconds at 473 K.

Resume : With the progress of epitaxial growth technology, complex oxide hetero-epitaxy attracts intense research interest due to the distinctive electrical, magnetic and optical properties which are not present in their bulk constituent. Lattice mismatch engineering can tailor the interplay between microstructure and properties of epitaxial-grown layers. In case of large lattice mismatch, defects like oxygen vacancies and misfit dislocations will appear for accommodating epitaxial strain. Therefore the development of an overall understanding about their occurrence and relevance toward electronic structure is of great significance. Here, by using a combination of aberration-corrected transmission electron microscopy imaging and electron energy-loss spectroscopy, we performed atomic-scale investigations of the microstructure and electronic structure of defects in a SrMnO3 (SMO) epitaxial thin film on SrTiO3 (STO) grown by pulsed-laser deposition. A wide distribution of defects with different morphologies varying from misfit dislocations to dislocation-associated trenches was observed. Simultaneously acquired atomically resolved high-angle annular dark-field and annular bright-field images were used to evaluate the microstructure of these defects and to analyze the strain state of the SMO thin film, demonstrating a concomitant strain release. The energy-loss near-edge structures of the O-K and Mn-L2,3 edges reveal a noticeable electronic structure variation in the vicinity of the defect core. The origin of the electronic structure evolution will be discussed.

Resume : The role of trivalent rare-earth dopants on the cerium oxidation state has been systematically studied by in situ photoemission spectroscopy with synchrotron radiation for 10 mol % rareearth doped epitaxial ceria films. It was found that dopant rare-earths with smaller ionic radius foster the formation of Ce3+ by releasing the stress strength induced by the cation substitution. With a decrease of the dopant ionic radius from La3+ to Yb3+ , the out-of-plane axis parameter of the crystal lattice decreases without introducing macroscopic defects. The high crystal quality of our films allowed us to comparatively study both the ionic conductivity and surface reactivity ruling out the influence of structural defects. The measured increase in the activation energy of films and their enhanced surface reactivity can be explained in terms of the dopant ionic radius effects on the Ce4+ ? Ce3+ reduction as a result of lattice relaxation. Such findings open new perspectives in designing ceria-based materials with tailored properties by choosing suitable cation substitution.[1] [1] Nan Yang, Pasquale Orgiani, Elisabetta Di Bartolomeo, Vittorio Foglietti, Piero Torelli, Anton V. Ievlev, Giorgio Rossi, Silvia Licoccia, Giuseppe Balestrino, Sergei V. Kalinin, and Carmela Aruta, J. Phys. Chem. C, 2017, 121, 8841?8849.

Resume : Current solid oxide cells (SOCs) require temperatures in the region of 1000°C to operate. This is primarily due to the fact that current generation SOC electrolytes, such as YSZ, require high temperatures for sufficient ionic diffusion of the oxide ions to occur. It has been suggested that replacing YSZ with samarium doped ceria (SDC) or gadolinium doped ceria (GDC) would reduce the operating temperature of SOFCs into the intermediate temperature range of 600-800°C, thus greatly reducing operating costs and increasing efficiency. It has been suggested that the strain which is induced in epitaxial thin films of these materials can result in enhancements in conductivity, though the degree of enhancement is often debated. There has been little theoretical investigation into oxide ion conductivity of SDC and GDC at surfaces and strained surfaces. Classical molecular dynamics simulations can be used to study the strain effects in these systems. We utilise a polarisable force field, known as the dipole polarisable ion model (DIPPIM), which has been derived from ab-initio data for ceria with a range of trivalent dopants. Biaxial tensile strains are applied to the (111), (221) and (210) slabs as this is a realistic representation of epitaxial thin film growth. We will discuss the effect of the surfaces and strained surfaces on the performance of SDC and GDC as oxide ion conductors. We have found that the ionic diffusion at the surface is highly surface dependent.

Resume : In multiferroics, the coupling between the different ferroic ordering phenomena opens the door for a large variety of applications, e.g. as sensors or in data storage devices. In this contribution we report on multiferroic composites consisting of BaTiO3 as ferroelectric component in combination with either ferrimagnetic ferrite spinels MFe2O4 (e.g. M = Co, Ni) or ferromagnetic metals/alloys (Ni, Co1/3Fe2/3). As an interface-mediated effect the magnetoelectric coupling strongly depends on the connectivity of the components. We have prepared 0?3 composites, i.e. particles of the ferro-/ferrimagnetic phase embedded in the BaTiO3 matrix, by a polyol-assisted synthesis followed by reductive sintering and mild reoxidation. On the other hand, the eutectic crystallization of CoFe2O4/BaTiO3 melts in an optical floating zone furnace leads to composites with 3?3-connectivity. A variety of different geometric structures with very smooth interfaces are formed by self-organization. All samples have been investigated with a broad spectrum of characterization techniques comprising XRD, SEM/EDX, impedance spectroscopy and temperature- and field-dependent magnetic measurements. The magnetoelectric coefficients have been studied in detail with respect to different compositions, temperature, external magnetic field and frequency.

Resume : There has been a lot of efforts to develop catalyst with better performance than platinum (Pt) in the low and medium temperature ranges as Pt is precious and expensive. Pt or Pt-alloys have been regarded as top performance catalysts for oxygen reduction reactions (ORRs) essential for a variety of electrochemical devices, including batteries, fuel cells, electrolyzers and gas filters. ORRs occur through sequential reactions in case of using oxygen ion conducting electrolytes and non-ion conducting metal catalysts: i) adsorption of oxygen gas on the catalyst surface, ii) formation of oxygen monomers to remove O-O bonds, iii) surface-transport of the O-monomers to charge transfer sites, iv) reduction and ionization of the O-monomers, and v) incorporation of oxygen ions into the electrolytes [1]. Among these steps, reduction of O-monomer is considered as the most energetically unfavorable reaction that determine the overall process rate. In this respect, maximizing triple phase boundaries (TPBs) where catalyst, electrolyte and space are in physical contact and the charge transfer of the O-monomer can occur is expected to significantly improve the ORR. Our approach is to decorate the surface of the metal catalyst with percolated ion-conducting oxide nano-particles to extend TPBs to the surface catalyst. As a metal-backbone catalyst that can replace platinum, silver (Ag) can be thought of because the ORR on the Ag surface has been reported to be as active as Pt in the intermediate temperature range [2,3]. Our group has tried doped zirconia (ZrO2) and ceria (CeOx) [4-6] as ion conductive nanoparticles. The performance of the Ag oxide composite catalyst was evaluated as the anode of a solid oxide fuel cell at temperatures of 300-500°C. As a result, we found that Ag with optimized scandia-doped ZrO2 (ScSZ) nanoparticles is superior to Pt in terms of fuel cell output, ORR impedance and long-term stability [6]. Ag catalysts containing yttria-doped ZrO2 (YSZ) nanoparticles showed comparable performance to Pt catalysts [4], while the performance of doped ceria was found to be far less than that [5]. In this presentation, we will discuss detailed performance of Ag-oxide nano-particle composite ORR catalysts and their underlying mechanisms. References (1) H. Uchida, M. Yoshida, and M. Watanabe, J. Electrochem. Soc. 1999, 146(1), 1. (2) T.-J. Huang, X.-D. Shen, C.-L. Chou, J. Power Sources 2009, 187, 348. (3) M. Gödickemeier, K. Sasaki, L. Gauckler, I. Riess, J. Electrochem. Soc. 1997, 144, 1635 (4) Y. K. Li, H. J. Choi, H. K. Kim, N. K. Chean, M. Kim, J. Koo, H. J. Jeong, D. Y. Jang, and J. H. Shim, J. Power Sources 2015, 295, 175. (5) K. C. Neoh, G. D. Han, M. Kim, J. W. Kim, H. J. Choi, S. W. Park and J. H.Shim, Nanotechnology 2016, 27, 185403. (6) H. J. Choi, M. Kim, K. C. Neoh, D. Y. Jang, H. J. Kim, J. M. Shin, G. Kim, and J. H. Shim, Adv. Energy Mater. 2016, 1601956.

Resume : Metal-Organic Frameworks (MOFs) are studied extensively in applications like catalysts, gas storage and sensors due to their various functional groups and porous structures. Two dimensional MOFs such as triphenylene-based materials show excellent charge transport property but thin film fabrication and organic ligand synthesis are difficult. In this work, we synthesize thiol-based organic ligand, benzenehexathiol (BHT), by a simple one-pot reaction. This facile method is safer and faster than conventional synthesis procedure which requires using liquid ammonia as solvent. We also demonstrate an efficient approach for fabrication of MOFs thin film by growing MOFs on functionalized substrates. Group 11 elements (Cu, Ag and Au) are used in this study to achieve planar coordination of metal ions and thiols in BHT. Functional group of silane on the substrate has affinity to BHT or metal ions, leading to high quality MOFs thin films. This general method can be used to control the growth of 2D MOFs on silicon substrate. Cu-BHT exhibits better redox performance in water than AgBHT and AuBHT. We fabricate a glucose sensor using 2D film of Cu-BHT that can sense 30mM glucose in water.

Resume : Among ceramic fuel cells, protonic ceramic fuel cells (PCFC) attract growing interest. Proton-conducting ceramic electrolytes offer a higher ionic conductivity compared to oxide ion conductors, in particular at intermediate T (300-600°C). Finding optimum cathode materials with mixed protonic and electronic conductivity is crucial for PCFC performance. So far, proton concentrations were measured only for few cathode materials, e.g. Ba0.5Sr0.5Fe0.8Zn0.2O3-delta [1]. They are significantly smaller than for BaZr1-xYxO3-x/2 electrolyte materials under comparable conditions. Recent first principles calculations for La1-xSrxFeO3-delta [2] yielded protonic defects (hydroxide ions on regular oxygen sites) with similar geometry as in BaZr1-xYxO3-x/2 electrolytes but much less negative hydration enthalpy. In the present study, we extend the calculations to nonstoichiometric Ba1-xSrxFeO3-delta and compare results from CRYSTAL (atomic basis) and VASP (plane waves) codes. Correlations of protonic defect formation energies with parameters such as ion charges, local atomic coordination and bond lengths are analyzed to obtain an atomistic understanding of the adjusting screws determining proton uptake in PCFC cathode materials. A comparison of proton migration and proton uptake with other cathode materials will be drawn and discussed. [1] D. Poetzsch, R. Merkle, J. Maier, Faraday Discussions 182 (2015) 129 [2] D. Gryaznov, R. Merkle, E. Kotomin, J. Maier, J. Mater. Chem. A 4 (2016) 13093

Resume : We present the synthesis and growth of iron phosphate polyanions films by a novel chemical method so called liquid phase deposition (LPD). LPD is a soft chemical method which was used initially for the thin film growth of metal oxides. This chemical technique is based on the slow hydrolysis of fluoro-metal complexes in the aqueous solutions by replacing the fluorine ions from the water soluble metal-fluoro complexes by OH- groups. Iron phosphate polyanion is known for its great applications as the cathode materials for the small ion batteries owing to their longer lifetime, better power density and high degree of safety compared to other cathode materials. Recently, our group has extended this method for the film growth of polyanionic compounds. Scanning electron microscopy (SEM) observations showed that the morphology, continuity and the phase composition of the films strongly depend on the deposition temperatures and the precursor concentrations. Those films grown at 60 and 75 °C with 4 dM of phosphor fluoro-complex concentration are highly uniform, free of cracks, pure and continuously cover the stainless substrates. Thickness of these films easily can be tailored in the range of 80 nm to 2.7 ?m simply by varying the deposition time. Finally, the electrochemical properties (cyclic voltammetry) of FePO4 films as cathodes for Li-ion battery applications on 316-stainless steel were investigated. Cyclic voltammetry analysis at 20 mV/s scan rate showed that pseudocapacitance of the films are thickness dependent and the maximum pseudocapacitance (72.8 F/g ) corresponds the films grown at 75 °C- 4 dM with 230nm thickness.

Resume : Major sources for human-made CO2 emissions comprise the energy and the industrial sector including cement production. One of the most appropriate concepts to capture CO2 is the oxyfuel combustion. However, most of known highly permeable membrane materials show unwanted chemical instability against CO2 and other flue gas components. Therefore, new advanced membrane materials and components are needed for such technological processes as the oxyfuel combustion. In the present study, oxygen permeation tests were performed, in order to study the effect of CO2 on surface properties of the (La,Sr)FeO3 perovskite membranes. A theoretical model was developed and applied to an analysis of the experimental data. The obtained CO2 adsorption enthalpies are compared with the results of hybrid density functional (DFT) calculations. Subsequently, the hybrid DFT calculations allow for a deeper atomistic understanding of the CO2 adsorption. This includes the correlation between the adsorption enthalpy and stability of different atomic configurations for the CO2 adsorption and membrane basic properties, such as the Fe oxidation state, a role of surface vacancies, bond lengths and bond populations. A good agreement between the DFT adsorption enthalpies and measured ones suggested an important role of oxygen vacancies and confirmed the formation of carbonate phases.

Resume : High temperature proton conductors (HTPCs) are promising materials for hydrogen energy conversion and storage. Among them acceptor doped lanthanum orthoniobate (LaNbO¬4¬) has total protonic conductivity reaching 10-3 S/cm at 900 °C. In our previous works we have shown antimony substitution on Nb site and its influence on structural properties and stability of the material. LaAsO4 also has been considered as proton conductor with total conductivity around 10-5 S/cm at 900°C. On this basis, it may be expected that LaSbO4 ? another member of the ABO4 group ? may also be considered as a potential candidate for proton conducting ceramics. Based on a few literature reports we have synthesized calcium doped LaSbO4 and LaAsO4 in order to study their proton conductivity. The materials have been thoroughly investigated, focusing on the influence of doping on electrical properties. Enhanced proton conductivity was expected due to A-site acceptor doping. Prepared samples were characterized by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM), Dilatometry measurements and Electrochemical Impedance Spectroscopy (EIS). XRD results show that single phase LaSbO4 can be formed. SEM images confirmed dense microstructure of obtained samples. In particular, electrical conductivity has been studied as a function of temperature and oxygen partial pressure. This work was financially supported by the National Science Center, Poland Grant No. 2015/17/N/ST5/02813.

Resume : Geologists have known for almost one century the existence of natural photochromic minerals of the sodalite family. Although the community is mainly trying to develop new type of photochromic materials, almost no efforts were devoted to understand and develop these natural minerals known by the geologists for a long time. In this presentation, we will focus on natural sulphur-doped sodalite mineral of Na8Al6Si6O24(Cl,S)2 that is computationally investigated for the first time, in order to understand its photochromic properties that are based on point defects. By combining periodic boundary conditions and embedded cluster-type approaches, we bring a theoretical overview on the photochromism mechanism. Our TD-DFT calculations of sodalite systems containing electrons trapped into chlorine vacancies (called F-center) showed absorption spectrum and a simulated color in agreement with experiment. This modelling highlights the huge effects of F-center?s environment such as the direct contribution of the ?-cage on the trapped electron and a strong vibronic coupling of the absorption spectrum. Post-Hartree-Fock calculations were also operated on S22--containing systems in order to determine the exact mechanism of coloration and discoloration, supporting that the key step is a direct through space charge-transfer between S22- ion and a chlorine vacancy. The geometry modification induced by this charge-transfer leads to a large electronic reorganization stabilizing the F-center thus explaining the high stability of the colored state of the mineral.[1] [1] A. Curutchet, T. Le Bahers, Inorg. Chem. 56, 414 (2017).

Resume : Solid polymer electrolyte films were prepared by mixing PEO-NaI with fine ball milled NASICON particles of NaTi2(PO4)3 [NTP] in the composition 10NaI-90(PEO1-XNTPX) (wt%) by solution casting. After removal of solvent, films were further treated in hot press at 70oC. The resulting free standing films were used for investigation by impedance spectroscopy. The bulk conductivity of the composite increases gradually with the NTP content and attain maximum conductivity ? 3 x 10-6 ?-1cm-1 for X = 0.4 at 40oC. The XRD and DSC results suggest gradual decrease of crystallinity with NTP addition and compliment the enhancement in conductivity. The FTIR spectra suggest no complexation of NTP with the host polymer. X-ray Absorption Near Edge Structure (XANES) spectra for Carbon (C) and Oxygen (O) K edge was obtained. For the compositions x ? 0.1, the O k-edge energy shifts towards higher energy with NTP. However, above this composition, the k-edge energy shows gradual decrease. These result suggest that for lower NTP content samples, the electrical transport should be attributed mainly to ion-chain coupling mechanism, but with the higher NTP content, the ionic migration is likely through NTP crystallites. The C k-edge energy does not exhibit any distinct shift with NTP content. This further suggests that the Carbon in the PEO does not interact with the cation of the salt. Our results suggest that XANES analysis can help in the understanding of ionic transport in polymer composites.

Resume : The color F centers (electron trapped in the halide vacancy) are very common defects in alkali halides, identified by means of the ESR and optical absorption/luminescence. In particular, their properties in fluorites (CaF2, SrF2 and BaF2) are very well studied and understood in detail. However, the manifestation of similar defects in binary oxides with fluorite structure (CeO2 or UO2) is debated for a long time. Recently, we successfully applied the Mollwo-Ivey rule (correlation between lattice constant and optical absorption energy) to explain similarity of optical properties of the F-type centers in alkali halides, alkaline earth oxides and sulfides with NaCl lattice structure [1]. In this study, we have performed similar comparative analysis of the F-type centers in alkaline earth halides and oxides with fluorite structure supported by detailed analysis of the literature. Special attention is paid to oxygen vacancies in CeO2. Obtained results and conclusions are supported by the first principles calculations of the atomic and electronic structure of defective oxides. [1] Popov, A. I., Kotomin, E. A., & Maier, J. (2010). Nucl Inst Meth B 268, 3084-3089.

Resume : Strain-induced fast ion conduction has been a research area of interest for nanoscale energy conversion and storage systems. However, because of significant discrepancies in the interpretation of strain effects, there remains a lack of understanding of how fast ionic transport can be achieved by strain effects and how strain can be controlled in a nanoscale system. In this study, we investigated strain effects on the ionic conductivity of Gd0.2Ce0.8O1.9-? (100) thin films under well controlled experimental conditions, in which errors due to the external environment could not intervene during the conductivity measurement. In order to avoid any interference from perpendicular-to-surface defects, such as grain boundaries, the ionic conductivity was measured in the out-of-plane direction by electrochemical impedance spectroscopy analysis. With varying film thickness, we found that a thicker film has lower activation energy of ionic conduction. In addition, careful strain analysis using both reciprocal space mapping and strain mapping in transmission electron microscopy shows that a thicker film has higher tensile strain than a thinner film. Furthermore, the tensile strain of thicker film was mostly developed near a grain boundary, which indicates that intrinsic strain is dominant rather than epitaxial or thermal strain during thin film deposition and growth via the Volmer?Weber (island) growth mode.

Resume : SrTiO3, a perovskite-type oxide, is one of the best investigated materials in solid state ionics and commonly used as a model material for many studies. The defect model of bulk SrTiO3 is well understood and the conductivity of bulk samples can be tailored by acceptor or donor doping, e.g. with Fe3+ or Nb5+ on the Ti4+ site. However, there are still many problems that have not been understood so far, including the electrochemical behavior of SrTiO3 thin films [1]. Different slightly Fe-doped thin films were prepared by pulsed laser deposition (PLD). The electrical conductivity was measured using Electrochemical Impedance Spectroscopy (EIS) and was found to be near the intrinsic point, independent of the Fe3+ dopant concentration. Measurements in different oxygen partial pressures and for different bias voltages revealed further strong deviations from the bulk behavior. Special attention was drawn to the relation between exact stoichiometry and electrical conductivity. The cation stoichiometry was varied by modifying the target composition, but also by different PLD parameters. A model linking the low conductivity to the stoichiometry of the thin films is presented, highlighting the impact of cation vacancies and the antisite defects on the electrical conductivity of Fe:SrTiO3. 1. Kubicek, M., et al., Resistive states in strontium titanate thin films: Bias effects and mechanisms at high and low temperature. Journal of Electroceramics, 2017: p. 1-13.

Resume : In the typical solid oxide fuel cell system, the interface of electrode between the electrolyte which is known as triple phase boundaries (TPBs) plays crucial role within the electrode reaction. Many researches focused on the modification of interface to enhance the interfacial reactivity. In this work, the Sm0.5Sr0.5CoO3-? (SSC) nanofiber structure is utilized as an electrode. Nanofiber structure have a great potential to be a next generation electrode structure with advanced properties such as larger surface area, facile gas diffusion, and continuous conduction pathway. However, one-dimensional structure of nanofiber structurally limits the contacts at interface which results in high interfacial resistance and sluggish electrochemical reaction. To overcome the issue, nanocrystalline and nano-wrinkled structure of Gd0.1Ce0.9O1.9 (GDC) functional layer is deposited in hundreds nanometer scale with electrostatic spray deposition technique. The optimized functional layer can reduce 70 % of electrochemical resistance than reference electrode without functional layer. Nanocrystalline and nano-wrinkled structure can provide extended active TPBs with higher density of grain boundaries and additional contacts, respectively. Here, we report the modified nanofiber electrode performs not only the enhanced performance, but also the modified reaction mechanism which can be confirmed by reduced activation energy from 1.63 to 1.31 eV substantiating that the interfacial issue is fully relieved.

Resume : In this work we investigated the effect of clay addition on various properties of proton conducting membranes of sulfonated polyether ether ketone) (sPEEK) for fuel cell application. We prepared our membranes by Doctor-blade casting technique including different loadings of two types of clay, a commercial montmorillonite and a home purified one, in the range of 5-20 wt%. We performed XRD, ion exchange capacity (IEC), water uptake (WU) and ionic conductivity measurements at various temperatures. The XRD patterns show the typical peaks of the clay confirming the effective introduction and the stability of the clay even after the thermal and the acid treatment of the membranes. The IEC measurements showed increased values by introducing the clay at around 5 wt% and a progressive reduction occurs with the increase of the clay amount. The WU reported at different temperatures showed different behaviours depending on the clay used. At 30° C and for the home clay, we observed a slight decrease in the WU value around 5Wt% and the values remain as a constant for all the superior amounts. At 80°C lower values than sPEEK sample are visible with the 5 and 15wt% while a slight increase occurs with the 10wt%. At 95°C the composite membrane having 5wt% of clay has the highest WU but a reduction is recorded by increasing the amount up to 15wt% and a further increase is visible with the 20wt%. For the commercial clay the behaviour at 30°C is the same but by increasing the temperature at 80°C we observe an increase in the WU with using 5 and 10 wt% and a successive reduction by increasing the loading up to 20wt%. At 95°C the trend is the same for both clays with the highest WU for 20wt%. the proton conductivity of composite membranes carried out at 100%RH as a function of temperature showed increased values with the increase of temperature up to 95°C and a drop at 120°C occurs due to the swelling effect that degrades the polymeric matrix and produces the drop of mechanical properties. The proton conductivity of the sPEEK is the highest in the whole range of investigated temperature and the introduction of clay reduces the conductivity. By comparing the evolution of proton conductivity of composite membranes containing various amounts of clay we observe a reduction at 60°C for 5, 10 and 20wt% only for the commercial clay composite and this trend is not observed for the home purified clay composite for which the conductivity increases until 95°C. As a conclusion of this work we found that the 15wt% loading permits the best compromise between chemical-physical and electrochemical data and for this it will be considered for our future fuel cell tests.

Resume : Study of physical and chemical properties of polycrystalline oxide materials requires consideration of properties related to the grains and boundaries between them. Isotope exchange method provides the necessary information on the kinetics of oxygen exchange with the oxide surface as well as the diffusion of oxygen. In this work, the oxygen isotope exchange with dense ceramic material La0.8Sr0.2MnO3±? is studied at a temperature of 850-950 °C and an oxygen pressure of 1 kPa. An approach to the analysis of oxygen diffusion routes in oxide polycrystalline materials based on the model for the GPE experimental data treatment taking into account the oxygen diffusion inside the grains and along the grain boundaries is proposed [1]. It is shown that when the oxygen diffusion coefficient in the grain volume Dgr exceeds the diffusion coefficient along the grain boundaries Dgb, the rate is determined by diffusion in the bulk of the grains. In this case, we can use the model of Klier et al [2]. In the case when the diffusion coefficient of oxygen along grain boundaries Dgb significantly exceeds the diffusion coefficient in the grain volume Dgr, it is possible to calculate two diffusion coefficients of oxygen using the developed model. The proposed approach is tested on experimental data on a polycrystalline oxide La0.8Sr0.2MnO3±?. The diffusion coefficients in the volume and along the grain boundaries are calculated. The value of Dgr agrees with the data of isotope profiling from literature. References: [1] L. Putilov, M. Ananyev. Abstr. SSI. 2015. D.2.20 [2] J. Phys. Chem. Sol. 27 (1966) 1087-1095 Acknowledgements: This work is partly financially supported by Scholarship of Russian President 2018-2020. The facilities of the shared access center ?Composition of Compounds? IHTE UB RAS were used in this work.

Resume : The incorporation reaction of oxygen into oxide materials proceeds via a complex network of reaction steps, and is expected to depend on the concentration of ionic (e.g. oxygen vacancies) as well as electronic defects (electrons, holes, mixed valent cations), see e.g. [1, 2]. Oxygen exchange is investigated by pulsed oxygen isotope exchange [3] on single and co-doped ceria containing 0.6-20 mol% of dopants: Gd3+ leading to oxygen vacancies formation, Pr3+/4+ creating oxygen vacancies and/or redox activity, and Nb5+ causing the formation of conduction electrons and/or oxygen interstitials. The equilibrium exchange rates are found to be low for Nb-doped and Nb/Pr-co-doped ceria. For Gd-doped ceria (GDC), exchange rates are proportional to the concentrations of Gd and oxygen vacancies. The pO2 dependence indicates that oxygen vacancies as well as molecular oxygen species are involved in the rate determining step. Pr-doped ceria (PDC) exhibits a much stronger variation of the exchange rate, emphasizing the importance of redox-active centers. The low formation rate of 16O18O on PDC compared to GDC points to enhanced oxygen vacancy diffusivity in PDC which is further investigated by SIMS. Measurements on Gd/Pr-co-doped ceria are in progress to deconvolute the impact of vacancies and electronic defects. [1] I. Riess, Solid State Ion. 2015, 280, 51. [2] M. M. Kuklja et al., Phys. Chem. Chem. Phys. 2013, 15, 5443. [3] H. J. M. Bouwmeester et al., Phys. Chem. Chem. Phys. 2009, 11, 9640.

Resume : (Ba?.?Sr?.?)(Co?.?Fe?.?)O? (BSCF) shows very high oxygen permeability [1], which makes it a promising material for oxygen separation membranes. However, secondary phases form at application-relevant temperatures below 850 °C, which degrades the oxygen permeability. One approach to stabilize the cubic BSCF phase is partial substitution of B-site cations. In this work Ti and Nb were investigated regarding their ability to suppress secondary phase formation. Our study focuses on microstructure of doped BSCF in dependence of temperature, doping level and 5% under-stoichiometric B-site occupation. Ti- and Nb-doped BSCF bulk samples were annealed at 600 °C, 700 °C and 800 °C for 10 days. Microstructural characterization was performed using scanning (transmission) electron microscopy in combination with energy dispersive X-ray spectroscopy for chemical analysis. The volume fraction of secondary phases (cobalt oxides, hexagonal BSCF, Ba???Co?O????(Co?O?) precipitates (BCO), Nb-rich precipitates) varies strongly as a function of Ti- and Nb-doping concentration and annealing temperature. Doping with 10% Ti or Nb reduces BCO and hexagonal phase formation. 5% B-site deficiency reduces the volume fraction of cobalt oxide precipitates, which act as nuclei for hexagonal BSCF formation. Most efficient in secondary phase suppression is substitution of 10% B-site cations by Nb in combination with 5% B-site deficiency. [1] Z. Shao et al., Journal of Membrane Science, 172 (2000) 177-188

Resume : The members of BaCe(Zr)O3 series of proton-conducting electrolytes possess high values of total and proton conductivity and good stability at the intermediate Zr content. The aim of this work was to investigate the electrochemically activity and long-term stability of air electrodes based on the Ca3Co4O9?? compound, well known for its excellent thermoelectric properties and resently proposed as a perspective SOFC cathode material, in contact with Y or Gd doped BaCe(Zr)O3 electrolytes. Particular attention was paid on the effect of the electrolyte composition, kind and amount of sintering aids and shunt effect of the electron conductivity in the electrolyte in oxidative conditions on the electrode performance. The Ca3Co4O9?? electrodes with a precious?metal-free collector developed in this work showed good adhesive properties and superiour polarization characteristics, which were measured on the symmetrical cells with dirrerent proton-conducting electrolytes (ASR values were equal to 0.14 ? 0.22 ? cm2 at 700 C). The most advantageous electrode-electrolyte pairs with an optimized sintering aid?s content were tested in wet air, at 700 oC during 1500 h. Testing of the electrodes in the SOFC-mode was successfully performed on the anode-supported single cells with BaCe0.8Gd0.2O3-? and BaCe0.5Zr0.3Y0.2O3-? thin film electrolytes (30 ?m). This work was supported by the UB RAS program, project 15-20-3-15.

Resume : In this work, BaO?SiO2?B2O3 glass with 5 ? 25 wt% of Bi2O3 are prepared by melt?quenching technique. The structure of Bi2O3?containing glasses is studied as a function of Bi2O3 content by IR spectra. Thermal properties of the glasses are obtained by dilatometer. Joining and crystallization of Bi2O3?containing glass sealants with solid oxide fuel cell electrolytes after test for 30 h at 800°C are investigated via both XRD and SEM?EDS. The thermal?mechanical stability of sealing interface is tested via thermal?quenching cycles from room temperature to 800°C for 30 times. The local structure of BaO?SiO2?B2O3 glass is totally changed with the addition of Bi2O3. Bi2O3 has a big effect on reducing a glass?transition temperature and a softening point, but maintains thermal expansion coefficient of BaO?SiO2?B2O3 glass. Barium aluminate (BaAl2O4), bismuth boron oxide (Bi45BO69) and unknown phases are crystallized in only 10 and 15 wt% Bi2O3?containing glasses. SEM micrographs reveal the presence of needle?like, rectangular, and irregular shape crystalline phases and remaining amorphous phase in all samples. The presence of irregular shape Ba?Bi aluminosilicate phase results in crack formation through and surround the crystals. The sealing interface remains intact although the crack propagation is observed after thermal cycles for 30 times. The possible mechanism on the phase evolution of the Bi2O3?containing glass?ceramics at the sealing interface is investigated and proposed.

Resume : The heterogeneous photocatalytic degradation of para-aminobenzoic acid (PABA), one of the components that are present in many types of PPCPs, has been investigated in aqueous solutions of Zinc oxide nanospheres using UV and Visible illumination. Zinc Oxide (ZnO) nanospheres were synthesized by an easy and low temperature method. ZnO was successfullly synthesized by an thermal aging process under 70oC for 1 hr using Zn acetate, distilled water and oxalix acid as precursors. The final powders was characterized by X-Ray powder diffraction technique, Field-Emission Scanning Electron Microscope and Uv-Vis Spectrometry and showed that pure ZnO is obtained and the morphology is spheres with diameter less than 50nm. ZnO spheres were also studied for photocatalytic degradation of PABA (para-aminobenzoic acid), under UV and Visible illumination. Optimal experimental conditions were 1gr/L of ZnO nanopowder in 20ppm PABA aqueous solution and 90% degradation was obtained under UV irradiation

Resume : Application specific morphology tuning of materials is essential for several engineering applications. Ceramic materials which are normally prepared as powders have to be consolidated and heat treated (sintered) to get the final product. To achieve critical control over morphology, the happenings at the initial stages of sintering and particle interfaces are important. These events can be studied by Molecular Dynamics (MD). MD requires the interaction between the atoms as input which will normally be given as interatomic potential. Bond valence (BV) method which has been proposed based on Pauling?s 2nd rule is applicable for all types of bonding. BV based Morse potential is relevant for ceramics which usually have mixed type of bonding. Barium tantalum oxynitride (BaTaO2N), a ceramic which finds use in photoactive and charge storage applications, has been modelled using the above mentioned potential along with the explicit addition of a Columbic repulsion interaction. The lattice parameter and bulk modulus predicted through computation are found to be in agreement with experimental values. Two particle model of BaTaO2N has been modelled using MD and found to have interesting observations. For particles size > 10nm, segregation of TaO phase at the interfaces has been observed which is in agreement with the experimental reports. And also, it is found that for particle sizes < 6nm, phase segregation and degassing of atoms are averted. Based on the above results, we extend our work on MD of BaTaO2N to multiparticle sintering model to study the actual sintering experiments; the resulting densification and morphological changes have been experimentally verified. BV based Morse potential plus Coulomb repulsion term has been proposed for modelling other complex ceramics (eg. oxynitrides) using MD.

Resume : Sustainable Economic Aquaculture From Autonomously Real-time Monitoring (SEA-FARM) requires a large-scale energy storage device capable of cycling 100% of its energy for a near infinite number of times. Dielectric capacitive storage provides the necessary power density and lifetime, but falls short when it comes to gravimetric energy storage. Ferroelectric ceramics have high dielectric constant, and polarization values but low breakdown field, while polymers have a low dielectric constant but high breakdown strength. The obvious solution is to make a composite of the two materials. However, in practice this has been difficult to obtain. The issue lies at the interface between ceramics and polymers which is natural incoherent, creating an array of defects. By modifying the interface using processes like polymer grafting, these defects can be eliminated. We use a thiol-alkene click chemistry approach to improve the gravimetric energy storage of dielectric capacitors. By designing a thermally and electronically stable polymer that is cured through UV processing, functionalized high dielectric constant nanoparticles are directly bonded into a high breakdown polymer matrix. We show that correctly chosen surface functionalization could dramatically increase the energy storage available in a dielectric capacitor by reducing the energy of free electrons. The nanocomposite formed has a higher breakdown and dielectric constant enhancing the energy density of the capacitors, making a superior dielectric.

Resume : Polycrystalline ZnO with double Schottky barriers at grain boundaries allow the ubiquitous application of varistors for surge protection. Admittance spectroscopy, i.e. measurements of conductance and capacitance as a function of temperature can reveal the deep levels in ZnO associated with the transition metal dopants. On the other hand, similarly as TiO2 system, cheap, abundant, and environmentally friendly ZnO system has been long studied as anodes in photoelectrochemical cells for water splitting. Nanostructured ZnO materials have been extensively studied, e.g., since they can be easily produced and the high performance is expected. However, mechanistic understanding is rather difficult to obtain from such studies, as there are many unknowns such as surface structure, reaction sites and area, transport paths etc. This work aims to study the fundamental properties of ZnO photoanodes by using single crystalline samples with well-defined crystallography from the bicrystalline samples previously prepared. Photoelectrochemical properties of these ZnO single crystalline anodes were studied in a lab-made PEC test station. In addition to DC photocurrent measurements wide-frequency range impedance spectroscopy was obtained, in contrast to conventional mono-frequency capacitance measurements for Mott-Schottky analysis. Havriliak-Negami capacitance function is employed to describe the Schottky capacitance affected by the distributed trap levels. Photoelectrochemical characteristics are compared with nanostructured thin film ZnO anodes. Possibility of the diffusion-recombination mechanism for the additional polarization effects, as recently reported for TiO2 nanorod photoanodes, is examined.

Resume : Quantum chemical methods, such as density functional theory (DFT), have become a useful tool to predict structural and electronic properties of solid state materials as well as the migration paths of the ionic charge carriers. In ideal materials with dilute concentration of charge carriers the macroscopic ionic conductivity can be derived directly from the microscopic ion motion. However, at non-dilute concentration the motion of ions is correlated and depends on the local environment, which could be influenced not only by the interaction of the charge carriers but also by the presence of dopant ions and other lattice defects. In this case the ionic conductivity is determined by the correlated motion of all charge carriers, which can be simulated by the Kinetic Monte Carlo (KMC) method. In this study we perform KMC simulations for different solid state materials with potential applicability as electrodes or electrolytes in batteries and fuel cells. The simulations are based on DFT derived migration and interaction energies, which are used to model the energy landscape for the migrating ions. The simulations comprise materials with oxygen, lithium or sodium ions as charge carriers. Ionic conductivities are obtained for various compositions and temperatures and the underlying migration mechanisms as well as the influence of defect interactions are evaluated. The simulation results can contribute to a deeper understanding of the transport properties and support their optimization.

Resume : Long-term degradation of the oxygen exchange activity of mixed conducting perovskite-type air electrodes is a key problem which limits the broad market introduction of solid oxide fuel cells (SOFCs) and solid oxide electrolyser cells (SOECs). Typical degradation mechanisms involve surface reactions with critical impurities (SO2, Cr, Si) and formation of inactive phases. Recently, the Sr-free material Pr0.8Ca0.2FeO3-? (PCF82) was shown to exhibit very fast oxygen exchange kinetics [1]. The present study investigates the long-term stability of PCF82 under ideal (O2-Ar atmosphere) and accelerated ageing (O2-Ar with 2 ppm SO2) conditions. In pure O2-Ar atmosphere PCF82 shows excellent stability of the chemical surface exchange coefficient of oxygen kchem = 6E-4 cm/s for 1000 h at 700°C. Due to the addition of 2 ppm SO2 only a moderate degradation occurs with kchem decreasing to 1E-4 cm/s during 1000 h. Results from post-test analyses by scanning (transmission) electron microscopy and X-ray photoelectron spectroscopy show S-rich secondary phases in the near-surface region. These inactive phases occur in relatively large but locally isolated crystals, whereas significant amounts of the surface area remain unaffected. The latter effect explains the high stability of the oxygen exchange kinetics of PCF82 against SO2-poisoning. [1] C. Berger, E. Bucher, A. Windischbacher, A.D. Boese, W. Sitte, Journal of Solid State Chemistry 259 (2018) 57.

Resume : Density functional theory (DFT) calculations within the generalized gradient approximation (GGA) were used to examine the behaviour of point defects in the cubic B(VI)O3 perovskite-type oxide, ReO3. Energies of reduction and of hydration were calculated, and the results are compared with literature data for ABO3 perovskite oxides. The activation energies of migration for O2?, H , Li , Na , K and H3O were also determined. The empty A site in ReO3 is found to be detrimental to oxide-ion migration by a vacancy mechanism as well as to proton migration by a Grotthuss mechanism. Na , K and H3O exhibit activation energies of migration higher than 2 eV, whereas Li is characterised by a very low migration barrier of 0.1 eV. Reasons for this behaviour are discussed. Our results suggest that H , O2?, and especially Li , are high mobile ions in ReO3. In general, our results have strong implications for the mechanisms of ion migration in ABO3 perovskite oxides.[1] Literature: [1] J. P. Parras, A. R. Genreith-Schriever, H. Zhang, M. T. Elm, T. Norby and R. A. De Souza, submitted.

Resume : In the search for high performance solid oxide fuel cells cathodes, understanding the mechanism and the limiting parameters of the oxygen exchange reaction is of great importance. Gas phase oxygen and point defects in the electrode are involved in these reactions. The defect concentrations, however, depend on electrode polarization as well as on oxygen partial pressure. The resulting complex relations between electrode polarization, pO2 and defect concentrations make it challenging to mechanistically analyze current voltage curves in terms of reaction orders. In this contribution we show how to take advantage of these interdependencies to separate the kinetic effects of gas phase oxygen and point defects. Counter-balancing pO2-induced defect concentration changes by applying a DC voltage allows studying the pO2 dependency of oxygen incorporation and evolution rates at constant defect concentrations. In a similar way, we use DC voltage to tune the defect concentrations while keeping the oxygen partial pressure constant. Applying this method of data analysis to current voltage measurements on thin La0.6Sr0.4FeO3-d films strongly suggests electron holes and oxygen vacancies as the rate limiting defects for the oxygen evolution and incorporation reactions respectively. A linear relation between oxygen incorporation rate and oxygen partial pressure suggests involvement of molecular oxygen species in the rate limiting step.

Resume : Dual-phase membranes of the percolating mixed-conducting oxides LSCF or LSM as an electronic conductor in GDC as an oxygen ion conductor matrix are under active development. Electrical conductivity relaxations have been used for the determination of chemical diffusivity and surface reactivity which determines the kinetics for the high performance oxygen transport membranes. Unlike conventional bar-shape samples for 4-probe conductivity, van der Pauw method applied to the disk samples in this work allows a systematic investigation on the effects of catalytic surface layers such as LSC. Conductivity relaxations were monitored upon change in the atmosphere between air and nitrogen. Instead of applying the solutions of the diffusion equation for the single phase which have issues, it is suggested to examine the Laplace-Fourier transform of the relaxation in time domain to the frequency domain as previously suggested by Boukamp et al. Frequency domain transformation had been made for the relaxation in Hebb-Wagner polarization cells and for pneumatochemical relaxations in hydrogen storage kinetics. Modification of the diffusion problems can be much easily and comprehensively performed using the transmission line models. Preliminary analysis using the relaxation time constants roughly estimated revealed that the relaxations generally faster in oxygen incorporation than in ex-corporation. They are found fastest at the LSCF threshold or conductivity threshold around 20 vol.%, while the slowest at the GDC concentration threshold or ionic conductivity threshold at 80 vol.% LSCF. The LSC coating is found to accelerate the kinetics, especially with oxygen excorporation.

Resume : For the highly non-stoichiometric BaBiO3-? electronic structure, conduction mechanism, oxygen non-stoichiometry and phase transitions are supposed to be closely related but overall understanding is not yet achieved. In this work, BaBiO3 was prepared from BaCO3 and Bi2O3 by a solid state reaction method. The sample was pressed into pellets and sintered at 800oC for 24 hours. Two types of electrodes (gold and silver) were applied. AC response of BBO bulk sample was measured for a wide range of temperature by using an electrical furnace, a heating stage and a cryostat. The dielectric and conductive properties indicate the characteristic transitions at the temperatures some of which correspond to the known structural phase transitions, which appear to be closely linked to the oxygen non-stoichiometry. Detailed examination of AC behavior in different temperature regions is expected to provide a valuable insight into conduction mechanism in relation to the phase transition and oxygen nonstoichiometry. Temperature-dependent conductivity is however poorly reproducible. X-ray diffraction showed the presence of cubic perovskite single phase in as-prepared samples in air but annealing in argon results in the distorted structures. Electrical properties are affected by the atmosphere even at low temperatures near room temperature. Indeed, clear mass relaxations were observed by TG even at room temperature. Chemical diffusivities are estimated from the mass relaxation behaviors of powder samples which can be compared to the conductivity relaxations of the bulk samples.

Resume : High-temperature lability of anion sublattice underlying the superionic conductivity is a characteristic feature of the crystals with fluorite structure. The data on coherent diffuse quasi-elastic neutron scattering show that strong anion sublattice disordering in a superionic state results in the formation of short-lived clusters containing anion interstitials and vacancies as well as displaced anions. Since the formation of cluster is connected with the dynamical disordering of anion sublattice, their existence at room temperature seems impossible. It has been revealed recently that the preheating to 600-1000°C and subsequent quenching of CaF2 single crystals induces the structured absorption in VUV-UV spectral range with a giant low-energy tail reaching the visible region [1]. Such absorption cannot be ascribed to local centers, while similar absorption spectra are typical for indirect semiconductors. In our opinion, the observed absorption is due to the clusters with radically reconstructed electron structure, with regard to that of a regular CaF2 lattice. The disordering of anion sublattice in preheated/quenched crystals manifests itself via color center formation under weak X-irradiation, while X-rays do not affect as-grown crystals. The similar clusters have been observed in SrF2 and BaF2 crystals as well. [1] A.I. Ryskin, P.P. Fedorov, N.T. Bagraev, A. Lushchik, E. Vasil?chenko, A.E. Angervaks, I. Kudryavtseva, J. Fluor. Chem. 200 (2017) 109-114.

Resume : Materials which change their defect chemistry with the oxygen partial pressure p(O2) are important materials for solid oxide fuel cells (SOFCs) or as sensors. Exact characterization of these materials over a large p(O2) range is desired in this field of research. Since properties such as oxygen non-stoichiometry and defect chemistry have a big influence on ionic and electronic conductivities, electrode design highly depends on how these properties change with different parameters like temperature and oxygen partial pressure. While p(O2) values from 1 to ~10-4 bar (gas mixing with O2) and ~10-20 to ~10-25 bar (mixing of H2 and H2O, p(O2) depending on the temperature) can be rather easily achieved, the range in between is very difficult to access. With inspiration from literature, an optimized high temperature measurement setup was constructed, which electrochemically pumps oxygen through an yttrium-stabilized zirconia (YSZ) tube to change the p(O2) inside the tube accordingly. With this setup, the range from 1 bar to way below 10-30 bar was successfully reached with excellent long-term stability. Impedance spectroscopy and 4-point Van-der-Pauw measurements were conducted to investigate the influence of p(O2) on the defect chemistry as well as oxygen exchange parameters (via fast p(O2) jumps) for lanthanum strontium ferrite La1-xSrxFeO3-? (LSF) and neodymium nickelate Nd2NiO4 ? (NNO).

Resume : Mixed ionic and electronic conducting (MIEC) perovskite oxides are important materials for energy applications such as solid oxide fuel cells (SOFCs). La0.6Sr0.4CoO3-? (LSC) is a highly active material for the oxygen reduction reaction. Introduction of lattice strain is a very powerful tool to further improve the oxygen ionic conductivity and the catalytic properties of the surface of LSC far beyond compositional optimization. In this work, LSC thin films were deposited by pulsed laser deposition on single crystalline substrates. By using different substrates, columnar polycrystalline thin films (MgO, yttria stabilized zirconia) and epitaxial thin films with either in-plane compressive strain (LaAlO3) or with in-plane tensile strain (SrTiO3) were deposited. Subsequently, oxygen isotope (18O) exchange experiments followed by ToF-SIMS profiling were used to establish highly resolved isotope maps and depth profiles for across-plane and in-plane geometry. Combining the measurements of the tracer diffusion coefficients gives important insight into the different influences of strain and grain boundaries on the concentration and mobility of oxygen vacancies in different directions of LSC thin films. While the oxygen vacancy concentration varies depending on the imposed strain, the hopping distance as well as grain boundary effects are different in-plane and across-plane for the same strain state.

Resume : Samaria - Doped Ceria thin films (Sm0.2Ce0.8O2-?) are studied as solid electrolytes having much higher ionic conductivity than yttria ? stabilized zirconia (YSZ) and gadolinia- doped ceria (CGO) electrolytes operating in intermediate temperature range 400 to 700 degrees. The study is focused on applications in micro-solid oxide fuel cells (µSOFC) and ? sensors. The selection of PLD control parameters were optimized to deposite dense, free cracks of SDC thin films on Si and quartz substrates at 500 degree. The morphology, structure and chemical composition of the obtained films were investigated by SEM, XPS and XRD techniques. Optical characterization was performed using Spectroscopic Ellipsometry and UV-VIS measurements. The electrical properties are measured at 400 degree in air. Key words: SDC thin films; PLD, µSOFC, oxygen sensors

Resume : We present the DFT calculations of elastic moduli of \ce{CeO2-Gd2O3}, viz. \ce{Ce$_{1-x}$Gd$_{x}$O$_{2-x/2}$} (CGO), considering both essentially random and C-type ordered oxygen---vacancy configurations, representing fluorite-like and C-type solid solutions, respectively. We show that fluorite and C-type phase differ in bulk modulus and elastic constants (e.g., the ground state C-type phase (x>0.27) has larger bulk modulus). This explains experimentally detected non-linearity (Yavo et al., Scripta Materialia 123, p. 86-89) of elastic moduli with concentration.

Resume : Ternary layer-chain TlGaS2 and TlInSe2 single crystals exhibit high photo- and roentgensensitivity making them well-suited for photoresistors and roentgendetectors. The study of physical properties of the TlGaS2, TlInSe2 compounds and solid solutions on their base are very important for establishing the relations between their compositions and properties. This offers the possibility of controlling the band gap, energy position of emission bands and electrical conductivity of such semiconductors. The purpose of present work was to investigate the influence of (TlGaS2)1-?(TlInSe2)? solid solutions compositions (x = 0-0.5) on their photo- and roentgensensitivity, ac ? electric, dielectric and optical properties. The single crystals of (TlGaS2)1-?(TlInSe2)? (? = 0?0,5) solid solutions have been grown up. The photoelectric, roentgendosimetric, dielectric and optical characteristics of the (TlGaS2)1-?(TlInSe2)? solid solutions with various compositions have been determined. The maximum and spectral range of photosensitivity were found to redshift as x increases from 0 to 0.5. Both the photo- and roentgensensitivity of the solid solutions are higher than those of pure TlGaS2. The nature of dielectric losses and the hopping mechanism of charge transport in the (TlGaS2)1-?(TlInSe2)? solid solutions were established from the experimental results on high-frequency dielectric measurements. The results of high-frequency dielectric measurements on obtained (TlGaS2)1-?(TlInSe2)? solid solutions provided an opportunity to evaluate the density of localized states at the Fermi level (NF), the average time of charge carrier hopping between localized states (?), average hopping distance (R), scattering of trap states near the Fermi level and concentration of deep traps (Nt) responsible for ac-conductivity. The temperature dependences of exciton peak position for various compositions (x = 0-0.3) are investigated in 77-180 K temperature interval. It was established that with increasing x in (TlGaS2)1-?(TlInSe2)? solid solutions the width of their forbidden gap decreases.

Resume : Understanding the ionic transport characteristics of the electrode materials closely related charging-discharging kinetics has been a long-sought-for but not a quite successful research objective, at least, in the case of many state-of-the-art cathode materials for lithium ion batteries. Superior sodium ion conductivity of NASICON structure should play an important role in the developing Na3V2(PO4)3 as cathode material for sodium ion batteries. With the insight obtained from Na3Sc2(PO4)3 this work aims to investigate the mixed-ionic-electronic conduction in Na3V2(PO4)3 in relation to the reversible thermal phenomena corresponding to order-disorder transitions within the sodium sub-network. Considerable ionic conductivity is evidenced in Na3V2(PO4)3 cathode material in the discharged reference state by the electrode polarization behavior and by the variation with the structural phase transitions similarly as recently observed in Na3Sc2(PO4)3. Therefore, similar sodium order-disorder mechanism for the structural phase transitions can be considered in Na3V2(PO4)3. To understand mixed-conduction better an electron-blocking symmetrical Hebb-Wagner cell is designed using the liquid sodium electrolyte held by the separators between bulk Na3V2(PO4)3 pellet and the sodium metal plates. Wide-frequency range spectra can provide the diffusion kinetics as well as mixed-ionic-electronic conduction characteristics by application of the generalized equivalent circuit for mixed conductors. Temperature dependence will be examined for the limited range due to the stability of the ion-blocking electrode consisting of the liquid sodium electrolyte and sodium metal.

Resume : Electrode kinetics plays an important role in a performance of the electrochemical devices. One of the most common methods for electrode kinetics study is electrochemical impedance spectroscopy. However there is no generally accepted approach to the impedance data analysis, and the choice of an equivalent circuit in each particular case may not be obvious. For detailed analysis it can be useful to measure rates of individual steps of electrode process by an independent method and, applying physical models, to estimate their contribution to the overall electrode impedance. In the present study electrochemical impedance spectroscopy and oxygen isotope exchange with gas phase equilibration methods were applied to investigate the electrode kinetics for the O2, La2NiO4 ? | Ce0.8Sm0.2O1.9 | La2NiO4 ?, O2 symmetrical cells with different electrode thickness and microstructure in the temperature range 600-800 °C and oxygen pressure range 0.2 - 16 kPa. The experiments were carried out in similar conditions in order to get complementary information by the two methods. Using values of oxygen exchange and diffusion coefficients obtained by the oxygen isotopic exchange method the contribution of these processes to the overall electrode impedance was estimated. Probable mechanisms of electrode processes are discussed. The study was financially supported by Russian Science Foundation, project No. 17-73-10196 using facilities of shared access center ?Composition of Compounds? of IHTE UB RAS.

Resume : Full parametric impedance analysis of AC response of a TiO2 photoanode in a PEC cell as a function of the potential and with the illumination condition has been performed, which comprises the depletion capacitance at the semiconductor-electrolyte junction following Mott-Schottky relation and the chemical capacitance in the electrode layer for the electron diffusion-recombination kinetics. All the parameters can be related to the spectral feature and physical interpretation made and implication discussed. Compatibility of the two physical mechanisms for the PEC impedance is to be noted and further examined. Importantly, well-defined Schottky capacitance can be successfully described by employing Havriliak-Negami capacitance function explained by the distributed trapping levels. Bisquert diffusion-recombination model can be applied with chemical capacitance in ideal capacitor elements, not in CPE, thus allowing the straightforward interpretation of the diffusivity and recombination rate constants. Interfacial Warburg impedance closely related to the bulk electrode parameters, is suggested to be generic in many electrochemical systems described by diffusion-recombination (reaction)-trapping mechanism.

Resume : The presence of interfaces can strongly affect ionic transport in many energy materials. A key effect is the segregation of charged defects to or from these interfaces, which is accompanied by the accumulation or depletion of mobile ions in adjacent space-charge regions. In materials with interfacial separations on the order of nanometers, space-charges are expected to overlap, producing nano-ionic effects, where mobile ion concentrations deviate from bulk values. This is predicted to cause large differences in ionic conductivities. Analyses of nano-ionic space-charge formation typically use a continuum Poisson-Boltzmann model, under simplifying constraints. This allows analytical solutions for properties such as charge-carrier concentrations to be derived, but these results may be sensitive to the approximations that make this analysis possible. We have used atomistic modelling and a numerical site-explicit 1D Poisson solver to model space charge formation between pairs of parallel grain boundaries in Gd-doped CeO2, a widely studied solid electrolyte with applications in solid-oxide fuel cells. Nanocrystalline Gd-doped ceria has been reported to have an ionic conductivity several orders of magnitude larger than samples with larger grain sizes. Our approach allows us to explicitly include a description of atomic scale structure in our model. We will present results for a range of CeO2 grain boundaries, and compare the resulting data to the predictions from conventional models.

Resume : Several energetical applications are known where yttria-stabilized zirconia (YSZ) and zirconia / multiwall carbon nanotube (MWCNT) composites were useful used as parts of solid oxide fuel cells (SOFC), photovoltaic solar cells, supercapacitor or hydrogen storage materials. The Ni ? YSZ cermets are widely accepted as anodic materials in SOFCs with high catalitic activity and electrical conductivity. Some research works showed the drawbacks in hydrocarbon fuels as carbon build-up, sulfur poisoning or low tolerance to redox cycling. These irreversible processes damage the microstructure of anodes and reduce the cell performance, therefore Ni-free anode materials are continously researched and developed to overcome these problems. In this work, the design of milled and sintered YSZ / MWCNT composites was studied. The detailed structural investigations confirmed the MWCNT clusters in all cases, while the best homogenization was obtained in the case of YSZ / 1 wt% MWCNT composite. The Raman measurements showed unanimously results with structural observations. The apparition of the G and D bands for all the composites at ~1589cm?1 and ~ 1356cm?1 confirmed the structural integrity of MWCNT after the milling process. The effect of attritor milling and spark plasma sintering (SPS) at 1200°C, 1300°C and 1400°C on the structural and thermo-mechanical properties of 8 mol% yttria-stabilized zirconia (8YSZ) composites with 1wt%, 5 wt% and 10 wt% MWCNTs addition has been investigated.

Resume : We report a new in situ measurement method to determine the kinetics of the oxygen reduction reaction (ORR) and oxygen incorporation into fluorite and perovskite type mixed conductors, PCO (PrxCe1-xO2-d) and STF (Sr(Ti1-xFex)O3-d). These materials are promising candidates for use as electrodes in SOFC, gas sensors, and oxygen storage materials involving an oxygen exchange reaction. However, the individual rate limiting reaction steps are not fully identified. Optically probing the oxidation state by absorption measurements is feasible for PCO and STF and can help to discern between surface and bulk rate limiting processes. Optical relaxation measurements have been used in the past for this purpose. For our optical impedance spectroscopy (OIS) only a small signal voltage perturbation is applied to pump oxygen in and out of the film electrochemically, thereby changing its absorption. This generalized electrochemical impedance spectroscopy (GEIS) technique comes with the benefits of superior signal to noise ratio and the toolbox of analysis techniques available for impedance data can be readily applied to the acquired measurement data. We will present OIS measurements on model thin films, demonstrate the basic modeling approach and discuss the obtained results. The investigation also includes the electrochemical impedance measured in parallel. We believe that this is a very promising approach to provide answers for some of the most challenging questions in solid state ionics. This work was supported by JSPS Core-to-Core Program, A. Advanced Research Networks.

Resume : The present work is devoted to the study of the energy and angular dependences of the secondary electron emission (SEE) coefficients, the reflection and absorption coefficients of light by the Ga0.5Al0.5As/GaAs film. Based on the analysis of the obtained results on the structure, emission and optical properties of thin GaAlAs/GaAs films, the following conclusions can be drawn: The band-energy parameters, emission properties and lattice parameters of thin films (d ? 50-100 Å) of GaAlAs obtained by MBE and ion implantation differ little from each other. In the case of films obtained by ion implantation, the crystallographic orientation of the film and the substrate are in good agreement with each other. The depth exit zone of the true-secondary electrons and photoelectron for GaAs is ~ 100-120 Å, and for the Ga0.5Al0.5As film it is 150-160 Å. The values of the coefficients ?, respectively, for GaAs and Ga0.5Al0.5As are practically identical, and the values of the true-secondary electrons coefficients ?m differ by 20-25%. The coefficient of light reflection K in the whole investigated wavelength region (both in the absorption region and in the region of maximum reflection) of GaAlAs was up to 2 times that of GaAs. The heating of the GaAlAs/GaAs system at T ? 600 0C for 5-10 min resulted in a slight decrease in K in the region of intense light absorption (? ? 580 nm). One of the reasons for this may be the presence of some excess Ga or As atoms in GaAlAs films.

Resume : As waste material from combustion, CO2 can be used to synthesize some useful hydrocarbons by electrochemical conversion. As theoretical studies have already shown this process could be enhanced by graphene supported copper particles making it possible to synthesize more than 30 different products. However before implementing this procedure in industrial scale certain specifications must be achieved e.g. the durability of the working electrode. In this work graphene sheet stacks (obtained by electrochemical exfoliation from waste graphite crucible) are incorporated into nitrocellulose matrix and copper structures are electrochemically deposited on the composite creating a conductive catalyst coated electrode (CCE) thick films with an average thickness below 40 µm. In addition to surface morphology, electrochemical analysis has been carried out focusing on the durability of prepared electrodes in CO2 saturated aqueous solutions. The cyclic voltammetry tests show that the prepared CCE can be successfully used as cathode material for continuous and sustainable electrochemical processes.

Resume : Tin dioxide (SnO2), as a n-type semiconductor with the large band energy gap of 3.6 eV at 300K, has appeared to be one of the most popular materials for gas sensing due to its excellent stability, high sensitivity, fast response, etc. Though the morphology, size, and surface permeability of nanomaterials can result in the superior gas sensing compared with their thin films and bulks, their easy-going self-aggregation is the barrier to explore the best performance. So looking for a satisfying approach for the ordered arrangement of nanosized building blocks into hierarchically porous or hollow structures is still attracting widely attention. In addition, doping metal ions, such as Co, Au, Pt, Cu, etc, is another effective way to enhance the gas sensing of metal oxide semiconductors. Here, two categories of novel sensor materials, pure SnO2 with hierarchical pagoda structures and different contents of Pt-doped 3D porous SnO2 with similar structures were synthesized by a hydrothermal method. And the latter, bearing the porous, hierarchical, and dopant effects synchronously, has been systematically examined for acetone gas sensing. As such, the comparative study of both materials and different contents of Pt doping have been performed to show the porous and doping effects in detail, which further indicate that the Pt-doped 3D porous SnO2 hierarchical structure can be optimized as a promising sensing material for the detection of acetone gas.

Resume : LLZ ceramic power and pellets were prepared by the typical ceramic process. As recently illustrated in detail, conventional brick-layer model is not satisfactory both in theory and in practice for the description of dispersive and overlapped responses of polycrystalline solid electrolytes with current-constriction effects due to the grain boundaries. Parallel networks of the complex dielectric functions have been shown to successfully describe the AC responses of polycrystalline sodium conductors over the wide temperature and frequency range with model parameters of well-defined physical significance only around ten in number. Strongly dispersive impedance response of polycrystalline lithium garnet oxide ionic conductors Li7La3Zr2O12 indicates well-defined capacitance effects where the relaxation behavior suggests the common mobile-charge-carrier origin. An equivalent circuit model with one total sample resistance component connected in parallel with three Havriliak-Negami dielectric functions can succinctly describe the frequency and temperature dependence and also distinguish three components originated from bulk and the current-constriction due to the grain boundaries and electrodes. The low frequency polarization is successfully described by a finite length Warburg impedance with an interfacial Warburg impedance. The transmission line parameters are also found to be closely associated with the bulk conduction mechanism. The feature is suggested to be generic in the electrode polarization of diverse solid electrolytes.

Resume : NO (Nitric oxide) is a common toxic gas generated by the exhaust of automobile engines and the production of fossil fuel power plants, which seriously endanger the environment and human health. However, as an important intermediate in the chemical industry, NO is a messenger and effector molecule. In addition, as a biomarker gas in some physiological and pathogenic processes, the detection of exhaled NO is a new promising and noninvasive way as well, for instance, in studies of lung diseases and asthma. So researching and developing a portable, low-cost, high sensitivity with a ppb-level, and high selectivity NO gas sensor is an emergent and challenge job. Here, x%wtIn2O3-y%wtNb2O5-WO3 films were deposited by pulsed laser deposition (PLD) as ppb level NO gas sensors. We found that 1% In2O3-1% Nb2O5-WO3 is superior to one element doped and undoped WO3 films. As to 100ppb NO, the 1% In2O3-WO3 film has the sensitivity of 4.1 at the best working temperature of 70?, while 1% Nb2O5-WO3 has the sensitivity of 43.0 at the 110?, which are better than undoped WO3 films with 1.7 sensitivity at 110?. Furthermore, 1% In2O3-1% Nb2O5-WO3 increase the sensitivity to 56.1 at 70? and its limit of detection is 20ppb with the sensitivity of 3.2. Additionally, the sensitivities of 100ppbNO2, 10ppm HCHO, 20ppmCO, 20ppmH2, and 20ppmNH3 at 70? are 2.2, 4.0, 3.7, 3.3, and 2.3, respectively. So, the 1% In2O3-1% Nb2O5-WO3 has the lower working temperature, ppb-level sensitivity, and high selectivity.

Resume : This work investigates ZnO thick films for gas sensing application. Zinc oxide nanoparticles were synthesised by a mechanochemical method using ZnCl2 and Na2CO3 as precursors and NaCl as a diluent. The ZnO samples obtained were washed with DI water to remove NaCl and thermal annealed at 400 °C for 2 hours. The crystallographic structure of the ZnO synthesized powders was characterized by X-ray diffraction and its structure and morphology using HRTEM and SEM. A viscous screen printing paste, was prepared by dispersion of ZnO synthesised nanoparticles in ethanol/ethylcellulose solution with terpineol as evaporation control agent. By using screen printing method, thick films of synthesized ZnO paste were deposited on glass substrate and sintered at 450°C for 30 minutes. After deposition, the ZnO film thickness was measured and the effects of structural and morphology of ZnO on gas sensing properties were studied. ZnO thick films were exposed to H2S at 20 ppm and the results show that these ZnO thick films have applications as H2S gas sensor.

Resume : In this study, the possibility of modifying the grain boundaries of strontium titanate by decoration has been investigated mainly by impedance spectroscopy and Seebeck coefficient measurements. The findings are discussed in the framework of defect chemistry and microstructure. Grain boundaries in SrTiO3 have been found to be notoriously positively charged, giving rise to a strong depression of p-type (increase of n-type) and even sharper depression of ion conductivity. It is hence of enormous interest to be able to modify nature and charge of the grain boundaries. For that purpose, La and Rb compound were chosen as decorating dopants. In the case of La, donor doping of the grain boundary core and at least of bulk-near regions occurs, depending on the preparation condition. We notice the formation of a secondary grain boundary phase which explains the unusual conductivity features. In contrast to La, the big Rb-ion is expected not to be incorporated and to confer an extra negative charge contribution to the grain boundary core. Indeed this is observed up to 3at.%, while the tendency inverts for larger percentages, indicating Rb then to be introduced interstitially. In the Rb-case the positive core charge is hence reduced, but was not inverted.

Resume : There are two common methods to measure the impedance response of only one electrode of a solid-state electrochemical cell, microelectrodes or a three-terminal configuration. In aqueous electrochemistry, three-terminal configurations are widely used, however, implementing this method in solid-state electrochemistry is highly non-trivial. This work summarizes, which method is most suitable for different applications. We show potential error sources and evaluate each of them quantitatively with special emphasis on their impact in thin film electrode measurements. Evaluation is done by means of finite elements analysis (FEA), electric circuit simulations and conducted measurements. Three potential error sources were identified as particularly crucial factors: (i) Asymmetric sample cells (ii) short circuit currents across the reference electrode (RE), (iii) Especially for highly resistive electrode, coupling capacitances between the three electrodes. These error sources can result in different measurement errors such as additional high frequency semicircles, additional low frequency semicircles, inductive loops and even more critical, erroneous electrode properties without indicating of additional features in the impedance spectrum. We propose a novel sample geometry, the ?wing geometry?, which was designed to minimize the measurement errors significantly, but still remains affordable and suitable for different applications.

Resume : Solid oxide fuel cell (SOFC) and solid oxide electrolyzer cell (SOEC) devices, which transform chemical into electrical energy and vice versa, have the potential to make a significant contribution to the efforts of overcoming future problems of the energy economy. An optimal functionality of the electrodes in such devices requires a high catalytic activity at their surfaces, i.e. the capability for chemisorption and dissociation of O2 molecules, charge transfer to O2?, and incorporation of O2? ions into vacant anion sites of the crystal structure. Promising materials regarding these requirements are perovskites (ABO3), with La, Ba or Sr ions on the A sites, and transition-metal ions (Mn, Fe, Co) on the B sites. Using density functional theory calculations with a Hubbard-U correction, we aim to shed light on the correlation between stoichiometry, point defect concentrations and experimental synthesis conditions in the perovskite system LaxSr1-xFeyMn1-yO3-d. The stability regions in the phase diagram and point defect concentrations were calculated taking into account image charge corrections. Employing defect equilibrium reactions and applying the charge neutrality condition, point defect concentrations were obtained for varying elemental chemical potentials, i.e., synthesis conditions. The sensitivity of the results on the choice of the Hubbard-U parameter will be discussed.

Resume : Ionic transport is of increasing significance to enable controlled interplay between technical and biological systems. It allows on one hand the realization of novel electronic devices (ionic resistors, transistor, and memristors) and on the other hand direct contacts to biological systems and individual cells with controlled electrochemical potential. Hydrogels like polyacrylamide (PAM) offer attractive properties as ionic transport media with structural biocompatibility. In biomedical applications artificial passive ionic channels of PAM can be used to adjust the ionic transport resistance, ion selectivity and thus ionic flux. Based on the thermodynamic diffusion process of the ions in the hydrophilic channel, the ionic resistance is determined by geometry and polymeric matrix. By applying voltage along the ionic channel the transport of the ions can be supported or restrained by the electrical field with respect to polarity. The incorporation of an ion selective fluorescent dye like N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide (MQAE) gives information of the transient distribution of chloride ions in the hydrogel channel by fluorescent spectroscopy, since PAM is transparent for excitation and emission. Furthermore, MQAE can be immobilized in the hydrogel and thus determining the transition time of drifting ions through hydrogel channels. Current investigation focus on manufacturing hydrogel microchannels and switchable network matrices.

Resume : With the upcoming development of all solid-state batteries, there are solid electrolytes available that reach ionic conductivities of the same level as their liquid counterparts. Solid polymer electrolytes can be combined with inorganic solid electrolytes and electrode materials to composite electrodes which promise high performance and durability. Interfaces in such composites play a crucial role as they contribute significantly to the inner resistance of the cell. PEO is a cheap and easy to process polymer, which already reaches good ionic conductivity at elevated temperatures, and is well suited as model material for interface studies. In this contribution we present results on the interfaces between PEO and LiCoO2 as well as PEO and Li. As interfaces are usually buried within the device, we used a surface science approach to study the interfaces based on model systems. For the LiCoO2/PEO interface investigation, the PEO was evaporated stepwise onto the LiCoO2, a methodology which can also be applied to the study of interfaces between PEO and inorganic solid-state electrolyte. Reaction layer formation takes mostly place at the anodic side, while the cathodic part is less reactive. Degradation is not only limited to the polymer, but also affects the salt, for example LiTSFI. Information gained by this method gives further insight in to the composition of the reaction layer and the origin of the interface resistance.

Resume : Electrochemical cells based on proton conducting ceramics (PCC) offer a number of potential electrochemical applications. Since proton is the ionic charge carrier, they are utilized in electrochemical devices in which hydrogen or hydrogen containing molecules are the main resources or products. It should also be noted that moderate operating temperatures and low partial oxygen pressure on the fuel electrode in PCCs are advantageous to prevent degradation of the components. One of the critical issues in realizing PCC devices, however, is to find promising materials for air electrode that demonstrate high conductivities and chemical stability. In this work, we focus on BaZrO3 based electrode candidates to be applied for PCCs based on Ba(Zr,Ce,Re)O3 electrolytes (Re: trivalent dopant). Powder specimens are synthesized by a conventional solid state reaction process and their fundamental properties, including structural analyses and electrical conductivities, are investigated. Based on the experimental results, their potentials as air electrodes will be discussed.

Resume : Ceria exhibits unique catalytic properties with numerous applications, ranging from water splitting to oxygen storage. Density functional theory calculations predict a strong dependence of oxygen vacancy formation energies for different CeO2 surface orientations. Particularly, the (100) surface is expected to have a lower oxygen vacancy formation energy than the (111) surface. It has also been shown, that it is possible to grow both (111) and (100) oriented CeO2 islands on Cu (111), by adjusting the Ce and O2 ratio during the growth. In the present work CeO2 islands with (111) and (100) surfaces are simultaneously grown in-situ onto a Cu (111) substrate. The island formation is observed and characterized with low energy electron microscopy (LEEM) and micro-LEED (low energy electron diffraction). Using laterally resolved x-ray absorption spectroscopy (XAS) performed in a photoemission electron microscope (PEEM) the reduction of Ceria in an H2 environment is observed in-situ and in real-time, directly comparing the reduction kinetics of the (111) and the (100) islands. Spectra of the Ce M5 edge show a more pronounced reduction of Ce for the (100) islands as compared to the simultaneously observed (111) orientation, unambiguously showing that the surface orientation of CeO2 has a profound impact on its catalytic properties. A DFT study tailored to the morphologies of ceria islands confirms the observed differences in surface thermodynamics of the different orientations.

Resume : For air quality monitoring thin film type selective sensing elements for volatile organic components (VOC) (1000-5000 ppm), carbon monoxide (CO) (50-1000 ppm), nitrogen dioxide (NO2) (0.1-5 ppm), and hydrocarbons (HCs) (100-1000 ppm) are in large demand. Identification of selective sensing materials for each of these gases remain a major problem as majority of conventional chemi-resistive sensing materials (viz. SnO2, ZnO, WO3 etc) are plagued with relatively higher operating temperature (~ 300oC), poor base-line stability (> 15%) during prolonged uses, cross-sensitivity towards these gases and moisture etc in real field application. In the present work we have demonstrated that chemical solution deposited lanthanum iron cobalt oxide (LFCO) thin films could be attractive candidate for selective CO sensing (in the concentration range between 5 to 500 ppm) at relatively lower operating temperature (175-250oC). Among all these test gases studied, it has been reported that at an operating temperature ~ 225oC, LFCO thin film sensing elements sense only CO gas (5-500 ppm) with a response % varying between 18-87% and response and recovery times varies in the range of 49 – 225 seconds and 94 – 852 seconds respectively. We have explained that the superior CO sensing characteristics of ABO3 type LFCO thin films are primarily governed by the ‘B’ site transition metal ions (Fe,Co). Also, the symmetry and coordination of A (La,Sr) and B site elements are lost on these perovskite surfaces, and as a result, the surface is saturated with adsorbed oxygen and hydroxyl ions. These adsorbed species make the perovskite surface catalytically active and thus, the CO oxidation is favorable at relatively lower operating temperature. A microcontroller based electronic circuit module with LCD display has been developed and the CO sensing characteristics of optimized thin film type LFCO sensing elements have been demonstrated and benchmarked with available commercial CO sensing elements. Keywords: Lanthanum iron cobalt oxide, thin film, carbon monoxide sensing

Resume : Carbon dioxide (CO2) has a wide variety of manmade and natural applications including but not limited to carbonating drinks, fire extinguishers, photosynthesis etc. However, it is a green house gas, and in atmosphere it absorbs infra-red energy and dissipates the heat to the surrounding to cause global warming. Two most important sources of CO2 in consumer related activities are road transportation and building heating, ventilation and air conditioning (HVAC) systems. In view to this, development of economical, indigenous CO2 monitoring system is highly desirable. It is extremely advantageous to use semiconducting metal oxide (SMO) based thin film gas sensors compare to other commercially available sensors due to low cost, small size, higher stability and selectivity. Some recent literature reports recommend that hetero-junction between ?n? and ?p? type of semiconducting oxide can enhance the response and selectivity of the test gases. But, very few literature reports exist which specify the factors effecting CO2 gas sensing using ?n?-?p? type multilayer thin films. In the present work we have demonstrated CO2 sensing properties and obtained the factors effecting CO2 sensing performance using SMO based hetero-structure multilayer thin film.

Resume : To date, studies into the effect of strain on the ionic conductivity of thin films and multilayers have focused on the so-called ?optimised? ionic conductors, such as Gd- or Sm-doped CeO2, but the results have been both controversial and inconstant. In addition, very little attention has been payed to the ?non-optimised? electrolytes where defect-defect interactions are much more significant. But as the defect association is much stronger for these materials a much larger modification in the conductivity due to strain may be possible. We have grown ?optimised? and ?non-optimised? doped-CeO2 epitaxial films by PLD on double buffered MgO substrates. The dopants used were La, Gd, and Yb, which represents significant differences in the defect association. The strain was varied by thermal annealing to relax the intrinsic strain occurring during growth. With increasing in-plane compressive strain, the conductivity of the films was reduced and the activation energy increased. The observed change is in excellent agreement with computational work, and consistent with other experimental findings. Furthermore we show that the effect is more pronounced for Yb-CeO2 than La- or Gd-CeO2, demonstrating that larger changes in the conductivity with strain can be obtained with ?non-optimised? dopant cations. We rationalise our findings using static force-field simulations, suggesting that the cause is due to a combination of changes in the migration barrier and vacancy-cation configuration.

Resume : In this work, the phase relationships in the ZnO?PbO?Bi2O3 system are studied by the thermodynamic method and X-ray phase analysis of the samples. Quasi-binary sections were determined and an isothermal cross section of the system was constructed at 298 K. A method for calculating the standard thermodynamic functions of the formed intermediate phases was tested. The thermodynamic characteristics of the ZnO?2PbO?Bi2O3 compound are calculated. For high-temperature oxide phases of the ZnO?PbO?Bi2O3 system, new thermodynamic databases were used by their critical estimation / optimization, taking into account the available experimental data on phase equilibria. A thermodynamic model of solutions was chosen, which reproduces all the phase equilibrium data of the ZnO?PbO?Bi2O3 system within experimental errors. The selected thermodynamic model was used for extrapolation in the temperature and composition region, where experimental data are not available. Thermodynamic calculations of phase equilibrium have been carried out, which are of interest for the preparation and thermal treatment of samples in the ZnO?PbO?Bi2O3 system. Operating conditions usually deviate from thermodynamic equilibrium, and the oxygen potential in the processing of samples is not established. In view of this, the calculated diagrams are intended to give the development engineers data on the trends and changes in the liquidus temperature, the degree of crystallization and the partial pressures of the volatile components as a function of temperature, composition, and oxygen potential. The calculated diagrams can also help identify variable processes in high-temperature oxides, which are important for industrial practice. Calculation and modeling significantly reduces the amount of experimental work that must be performed for optimization of operations.

Resume : The GaS compound is a layered semiconductor with the indirect band gap of ~2.6 eV. The direct and indirect band gaps are separated by ~0.45 eV energy range. GaS single crystals consist of elementary packings (S-Ga-Ga-S) linked by weak polarization forces. Bonds of ionic-covalent nature act between atoms within the packings. The specific crystal structure allows the obtaining of parallel lamella with nanometric thicknesses, by single crystals cleavage. The Ga2O3 nanometric layers were obtained onto GaS lamella surface, perpendicular to the C6 crystallographic axis, by thermal annealing (TA) in atmosphere. The structure, morphology and optical properties were studied by XRD method, AFM microscopy, Raman and absorption spectroscopies, and also light scattering spectroscopy in the fundamental absorption edge region of both ?-GaS and Ga2O3 compounds. XRD patterns contain two types of lines: intense, with narrow contour, assigned to the (002) and (004) planes of ?-GaS crystal, and low intensity lines, with wide contour, characteristic for the (002), (111) and (311) planes of Ga2O3 oxide. There, also, the lines from the (110) and (300) atomic planes of Ga2S3 crystals are slightly highlighted. Thus, on the basis of the XRD analysis, it can be admitted that as a result of the GaS lamella TA in atmosphere, a composite consisting of GaS lamellae, Ga2O3 nanolamella, and traces of Ga2S3, is formed. The formation of Ga2O3 phase is also confirmed by Raman spectroscopy.

Resume : Purely organic conjugated microporous polymers (CMPs) are gaining an importance as materials for organic electronics, energy storage and photocatalysis. Accordingly, we have previously developed band-gap-tuneable donor?acceptor (D-A) sulfur- and nitrogen-containing polymers (SNPs) as a subclass of CMPs via Sonogashira?Hagihara cross-coupling. Due to open pore structure these materials can be easily modified by post-synthetic p-doping with iodine, and show good results in photocatalytic water splitting. Here, we used Pd-catalysed Stilled coupling to synthesise eight new materials to increase our knowledge about D-A polymers and expand the library of SNPs. As for electron-donor motifs we used four thiophene-based linkers: thienothiophene, dithiophene, benzotrithiophene, and naphthodithiophene. From the other hand, triazine ring, a key building block of covalent triazine-based frameworks, is known to be a good electron-acceptor. Commercially available cyanuric chloride and easy-to-synthesise tris-bromophenyltriazine were used as a source of triazine core. All materials are highly fluorescent and have mixed micro-/mesoporous structure with Brunauer?Emmet?Teller specific surface area and CO2 uptake up to 656 m2g-1 and 2,04 mmolg-1 respectively. The combination of ?-conjugated structure as well as D-A nature allows the control over the optical band-gap in the resulting materials (from 2.28 eV to 2.60 eV). Moreover, prepared SNPs can be used as fluorescence-on and fluorescence-off sensors for organic volatile compounds detecting. References. D. Schwarz, Y. S. Kochergin, A. Acharjya, A. Ichangi, M. V. Opanasenko, J. ?ejka, U. Lappan, P. Arki, J. He, J. Schmidt, P. Nachtigall, A. Thomas, J. Tarábek and M. J. Bojdys, Chem. - Eur. J., 2017, 23, 13023-13027.

Resume : Sodium bismuth titanate (NBT) recently has drawn immense research interest as a fast oxygen-ion conductor because of its high oxide-ion conductivity comparable with the other state-of-art materials like Gd0.10Ce0.90O2-?. Non-stoichiometric NBT compositions with Na/Bi molar ratio >1 exhibit at least three orders of higher conductivity than that of compositions having this ratio less than unity. In our recent work, we have shown that replacing Na for A-site Bi can lead to a significant conductivity enhancement. The present work aims to investigate the phase stability and conductivity behaviour on doping divalent and trivalent cations at the B-site in Na0.54Bi0.46TiO3-?. The conventional solid oxide route was used to fabricate the dense polycrystalline samples of Na0.54Bi0.46T1-xMxO3-? (M = Mg2 and Ga3 ). XRD indicated the presence of distorted perovskite rhombohedral structure in all the samples. SEM revealed the presence of secondary phases of Na2Ti6O13 and other compounds. Impedance spectroscopy showed improvement in grain conductivity on Mg2 doping in Na0.54Bi0.46TiO3-?, while Ga3 substitution leads to a monotonous lowering of conductivity. Among the tested compositions, the maximum grain conductivity of ~14 mS.cm-1 was observed at 600oC in air. The conductivity results and the ageing behaviour of Na0.54Bi0.46T1-xMxO3- ? at 600oC in air and reducing conditions will be presented.

Resume : Oxide epitaxial heterointerfaces possess a number of fascinating properties, spanning from superior electrical conductivity to magnetism, which do not belong to the constituting phases and which result from the interplay between different local phenomena. In this contribution, we present a study on the fascinating properties arising at the contact between lanthanum cuprate (La2CuO4) and Sr-doped lanthanum nickelate (La2-xSrxNiO4), which have been investigated in MBE-grown bilayers and superlattice systems. We show that high-temperature superconductivity arises in La2CuO4 within a nm-region at the interface (with superconducting critical temperature Tc up to 40 K) and that such a property can be tuned as a function of the supercell structural parameters, i.e. doping level in the nickelate, supercell thickness and layers sequencing. By employing a number of complementary techniques, including electrical conductivity measurement, aberration-corrected scanning transmission electron microscopy and spectroscopy, we were able to correlate the system functionalities with the local interface chemistry. This allowed us to propose a mechanism for local high-temperature superconductivity in the light of a generalized space-charge theory for oxide systems, which accounts of both ionic and electronic redistribution effects.

Resume : The perovskite-like oxide SrFe0.8Mo0.2O3-? is shown to combine valuable characteristics allowed utilizing it for the development of novel oxygen permeable membrane materials. The serious drawback of this material is related to poor sintering at ceramic processing. It is well known that partial substitution of Sr by La is beneficial for improved sinterability and densification of the ferrous ceramics. This work was focused on studying of lanthanum concentration influence on ceramic and transport properties of Sr1-xLaxFe0.8Mo0.2O3-?. Complex oxides Sr1-xLaxFe0.8Mo0.2O3-?, where x=0.05, 0.1 and 0.2, were prepared by glycine-nitrate synthesis. X-ray powder diffraction of Sr1-xLaxFe0.8Mo0.2O3-? show formation of single phase samples with cubic structure (s.g. Pm3-m). According to the thermal properties measurements in air, partial substitution of strontium by lanthanum results in a decrease of oxygen content variations at heating and respective improvement of thermomechanical properties. Analysis of electrical conductivity measurements carried out in the oxygen pressure range of 10-18-0.3 atm at temperatures 750-950ºC reveals increase of n-type electron conductivity in response to increasing lanthanum concentration in Sr1-xLaxFe0.8Mo0.2O3-?. Gas-tight tubular membranes were successfully fabricated from Sr0.8La0.2Fe0.8Mo0.2O3-?. This work was supported by the RFBR (grant 17-08-01029).

Resume : Zirconia nanopowders doped with subvalent ions have attracted considerable attention due to their mechanical, electrical, thermal and luminescent properties offering diverse applications such as catalysts, solid oxide fuel cells, high temperature resistant coatings, biological labeling, etc. In the most cases, to prepare zirconia-based powders, zirconium oxychloride is used. In the present paper we will demonstrate the effect of chlorine on spatial distribution of subvalent dopants and oxygen vacancies? content in Cu-doped Y-stabilized ZrO2 nanopowders prepared by co-precipitation technique. This effect was studied versus calcination temperature and Cu content. Zirconium oxychloride was used as Zr-based precursor. Optical and structural properties of the powders were studied using diffuse and attenuated total reflectances as well as XRD, EPR and Auger spectroscopy methods. It was observed that the increase of calcination temperature stimulates structure transformation, variation of oxygen vacancies content in the grains and amount of dispersed CuO at their surface. These changes depend on Cu content being controlled by surface-volume copper redistribution (copper in- and out-diffusion) and transformation of surface entities. At low Cu content, the amount of oxygen vacancies and CuO varies significantly and non-monotonically with temperature rise, while for higher Cu content, they changes slightly. The presence of chlorine inside ZrO2 grains was detected. This allowed assuming that slow formation of oxygen vacancies is due to Cl action as compensator for Cu charge. Besides, tight Cu-Cl interaction keeps Cu ions inside the grains that affects significantly the formation of CuO at their surface. The latter reduces the catalytic activity of the powders in the CO PROX reaction.

Resume : In doped systems of electroceramics, the presence of grain boundaries leads to defect redistributions, resulting in important material property changes. Conventional space charge theories have been established to model compositional changes near grain boundaries, based on the assumption of dilute dopant level. The fact that concentrated doped systems are widely employed in solid oxide fuel cells and other applications, demands a novel methodology that could be applied for these systems, where the premise of conventional models couldn’t be satisfied. Based on a thermodynamic framework of the Poisson-Cahn theory, a unified methodology has been developed to treat doped systems of all concentrations, expanding from the simplest case without defect interactions and gradient contributions to the more complicated cases where both effects become significant. The functional forms of defect interactions and gradient energy contributions are built through Bayesian calibration with discrepancy functions using EELS data of CaO doped ceria.

Resume : Perovskite-based materials have been widely studied as the electrode materials for high temperature electrochemical systems such as solid oxide fuel cells and solid state electrolysis cells, and other low-temperature electrochemical devices such as alkaline membrane fuel cells and metal?air batteries. While many perovskite-based electrodes have shown remarkable performance, cation segregation near the surface or interfaces is often observed, which greatly impacts not only electrode kinetics but also their durability and operational lifespan. The segregation of A-site alkaline earth metal oxides was reported to degrade the electrochemical performance in literature. In contrast, the segregation or exsolution of B-site transition metals and the formation of metal/oxide interface were found to significantly enhance catalyst activities and stability for the electrodes. Despite of many corresponding examples, contradicting results were reported in literature. A detail understanding of the correlation between the surface cation composition and the electrochemical reaction kinetics near the surface and interface is vital to achieving the rational design of more efficient perovskite based electrode materials with excellent durability. In this study, we aimed to provide critical insights into the mechanisms of cation segregation and provide the guide line for how to enhance desired positive effects while suppressing negative effects associated with cation segregation under operating conditions. (La,Sr)MO3 (M is the transition metal) thin films grown by pulsed laser deposition were used as model systems. The evolution of surface cation composition, morphology and local electronic structure as a function of temperature, gas environment and electric potential were systematic investigated. We observed the segregation of Sr on the surface of (La,Sr)(Fe,Co)O3 (LSCF) thin films after long time operation in oxygen environment at high temperature (500 to 600o C), which lead to the degradation of oxygen reduction reaction (ORR) activity. After the deposition of PrxCe1-xOy (PCO, x=0, 0.2, 1) surface modification layer, both the ORR activity and stability of LSCF were greatly enhanced. Based on SEM, XPS and TEM measurements, we believe such enhancement is partly due to the suppression of A-site metal Sr segregation on LSCF surface by the top PCO layer at elevated temperature. Furthermore, the surface modification was found to change the rate limiting step of ORR on the surface, which was attributed to the change of surface electronic structure as quantified by in-situ scanning tunneling microscopy/spectroscopy. By annealing in reducing condition or applying an cathodic potential, the exsolution of B site cation was observed on the surface of (La,Sr)MO3 (M=Ni,Fe,Ti) oxide. The local electronic structure changes introduced by B site exsolution were studied in details and were correlated to the catalytic activity enhancement.

Resume : Formation of NO which is toxic to human body and environment, is mainly occurred from combustion engines and so, removal of NO from exhaust gas is highly important issue at present. There are several methods reported for NO removal and among them, NO direct decomposition is the most ideal reaction because no reductant is required. In spite of spontaneous reaction, the active catalyst for NO decomposition is limited and low activity because of the deactivation of catalyst by the formed oxygen. In our previous study, we found that Ba doped Y2O3 shows high activity to NO decomposition, however, high reaction temperature is essentially required. In this study, effects of oxygen vacancy introduced into Er doped Y2O3 lattice by high pressure torsion treatment on NO decomposition activity were investigated. The high pressure torsion (HPT) is an effective technique for stabilizing high-pressure phases at ambient pressure and introducing oxygen vacancy effectively. Starting material was Y2O3 powder with 1 mol% Eu2O3. The HPT treatment was performed at room temperature by using around 0.2 g powder and applied at upper anvil for 1 turns. Plastic strain was introduced at 3 or 6 GP. Pulsed reaction was used for NO decomposition activity coupled with an online gas analyser. NO (1% in He) was subsequently introduced into the reactor to assess NO adsorption and decomposition. An online mass spectrometric detector was used to monitor the signals at m/z values of 28 (N2), 30 (NO), 32 (O2) and 44 (N2O). Although N2 formation was observed at initial few pulses on Er doped Y2O3 without HPT, NO decomposition was significantly deactivated. On the other hand, N2 and N2O yield was much increased by application of HPT treatment which could introduce oxygen vacancy and grain boundary, and N2 formation was stably observed over few 10 NO pulses. Therefore, oxygen vacancy might be work as active site for NO decomposition and increase in oxygen vacancy. Among the samples at different HTP treatment, Y2O3 by HTP at 3GPa shows the highest NO decomposition activity. However, O2 desorption was not observed and this could be explained that only increase in oxygen vacancy is not enough for increasing NO decomposition activity but also diffusivity in oxygen vacancy is essential for increasing NO decomposition activity in low temperature range. Effects of oxygen vacancy on NO adsorption state will be discussed in details based on FT-IR measurement.

Resume : Epitaxial interfaces in oxides have been extensively studied recently. One of the most intriguing interface effects is high-temperature interfacial superconductivity (HT-IS). In this study, La2CuO4-based bilayers were grown by oxide molecular beam epitaxy. They consist of a metallic (M) and an insulating (I) phase. The bilayers exhibit HT-IS up to ?40 K. To assess the role of dopant size on chemistry and superconductivity at the interfaces, different dopants (Ca, Sr, and Ba) were employed in the M-phase, and the M-I bilayers were investigated by complementary techniques, including analytical scanning transmission electron microscopy (STEM). Structural quality and perfect coherent interfaces were revealed via high-angle annular dark-field STEM imaging. The dopant distribution was studied via electron energy-loss spectroscopy and dopants were found to be inhomogeneously distributed in the M layer revealing distinct differences among the three dopant species. Annular bright-field STEM imaging provided quantitative information on octahedral distortions and yielded different Jahn-Teller (JT) and anti-JT effects. A series of exciting findings are highlighted: (i) the c-lattice parameter of the bilayers is linearly dependent on the ionic size, while dopant-specific redistribution is found at the interfaces, (ii) superconductivity is highly dependent on the dopant, and (iii) the dopant distribution has a remarkable effect on the JT and anti-JT distortions.

Resume : Numerous electroceramic devices, such as MLCCs (multilayer ceramic capacitors) or PTCR thermistors (positive temperature coefficient of resistivity), are based on barium titanate. The PTC effect (steep increase of resistivity above the Curie point) is associated with highly conductive grains and blocking grain boundaries. Usually, this behaviour is found in the case of small dopant concentrations and fairly large grain sizes around 3 ? 5 µm, if the ceramics are sintered in air. The electrical properties of donor and acceptor co-doped BaTiO3 ceramics have been investigated as a function of oxygen partial pressure and temperature (from room temperature to 900°C) by application of impedance spectroscopy. While samples doped with 0.25% La and 0.05% Mn or commercial specimens (doped with 0.5% Y and 0.1% Mn) show the PTC effect, samples containing fairly large amounts of donors and acceptors, e.g. 2.1% La and 1.0% Mn, are highly resistive at room temperature with Arrhenius-type temperature dependence of the bulk conductivity. In addition, BaTiO3 (doped with 0.25% La and 0.05% Mn) with grain sizes in the sub-micron range (200 ? 300 nm) is highly resistive with Arrhenius-type temperature dependence, most probably because of low calcination and sintering temperatures in order to avoid grain growth. The experimental results are interpreted in terms of defect chemical models for the bulk emphasizing ionic and electronic compensation mechanisms as well as the trapping effect of Mn.

Resume : Yttrium doped BaZrO3 combines a high bulk proton conductivity with good chemical stability [1]. Acceptor doping, e.g. by Y3+, Sc3+, leads to oxygen vacancy formation, which allows for dissociative water incorporation. Recently, dry and hydrated BaZrO3:Y was investigated regarding its unusual electromechanical properties. Due to the cubic symmetry of the material, piezoelectricity is absent but electrostriction (the second order quadratic effect linking strain and electric field squared) could still be observed, and was found to be exceptionally high [2]. In this presentation, DFT calculations of elastic and dielectric properties of Y:BaZrO3 and Sc:BaZrO3 are discussed. The obtained Young?s moduli in dry and hydrated state are in good agreement with experimental data. Their dependencies on dopant type and concentration are decomposed into contributions from modified lattice constant and modification of the lattice by defects (acceptors, oxygen vacancies, protonic defects). Finally, a mechanism is discussed in which the response of point defect clusters to an external electric field causes a macroscopic strain that could, in principle, explain the observed high electrostriction coefficient. Funding by GIF (grant no. I-76-302.1-2015) is acknowledged. [1] K. D. Kreuer, Annu. Rev. Mater. Res. 33, 333-59 (2003) [2] N. Yavo, O. Yeheskel, E. Wachtel, A. Frenkel and I. Lubomirsky, abstract for Solid State Ionics Conference, Padua, Italy (2017)

Resume : Recently we have demonstrated that I?V characteristics of grain boundaries in prominent solid oxygen or proton conductors can be accurately described using a simple linear diffusion formalism (I-V model).[1-3] The model assumes that: (1) the grain boundaries do not represent physical blocking layers and (2) the ions follow Boltzmann distribution. Despite its simplicity, the model successfully reproduces the ??power law??: current proportional to voltage power Igb~(Ugb)^n. The model also correctly predicts that the product n·T, where T is the temperature in K, is constant and is proportional to the grain boundary potential, ?gb. Previously, the value of ?gb has been determined exclusively by the ratio of an effective resistivity of a single grain boundary to that of grain interior (RR model[4]). This approach assumes that the grain boundary resistance arises solely from the depletion of charge carriers in the space charge zone. However, it may have various sources causing the RR model to overestimate the value of ?gb. We demonstrate that using the I-V model, ?gb can be determined accurately even if multiple factors are responsible for the resistance. Funding by US-Israel BSF (grant no. 2016006) is acknowledged. [1] S. K. Kim, et al., Phys Chem Chem Phys 2013, 15, 8716 [2] S. K. Kim, et al., Phys Chem Chem Phys 2014, 16, 14961 [3] S. Kim, et al., Phys Chem Chem Phys 2016, 18, 3023 [4] J. Fleig, et al., J. Appl. Phys. 2000, 87, 2372

Resume : Oxygen hyper-stoichiometric CeNbO4+d fergusonite is reported to possess high ionic conductivity at intermediate temperatures, making it a new class of ionic conductor for energy generation and storage purposes. This provides an alternative to more commonly used perovskite and fluorite electrolytes that heavily depend on vacancy migration. In order to explore the oxygen migration dynamics in fergusonite, defect crystallography needs to be understood. We successfully grew a single crystal of CeNbO4.25 using a floating zone mirror furnace and modelled the long-range average structure by analysing the single crystal X-ray diffraction pattern, neutron and synchrotron X-ray powder diffraction data, and electron diffraction. In addition to better capture the short-range coordination environment especially around the interstitial defect sites, pair distribution function (PDF) analysis of neutron powder diffraction data was performed. The combined diffraction results show that the structure has to accommodate the interstitials by modulating the oxygen positions commensurately, creating a ~12 times larger cell with cell vectors given by the following matrix: (ar, br, cr) = (2, 0, 2 | 0, 2, 0 | -2, 0, 1) (ap, bp, cp); where the (a,b,c)r and (a,b,c)p are the resultant supercell and stoichiometric (d = 0) cell lattice vectors, respectively. The ordering of Ce3+ and Ce4+ was discovered with a continuous helical network of Ce4+Ox running parallel to the crystallographic z- axis. In addition, the coordination number of Nb expands from 6 to 7 or 8.1 To validate the experimental findings, the oxygen migration was simulated using molecular dynamics approach based on the determined superlattice. CeNbO4.25 shows significantly greater mean square displacements of oxygen at 1073K than does CeNbO4; this indicates that the interstitial oxygen ions are mobile. At higher temperature (1573 K and above), the major migration pathway lies within the NbOx polyhedra slab (xz plane), but with some connectivity along the y crystallographic axis being observed, consistent with the existence of NbO7 and NbO8. The calculated activation energies for oxygen diffusion (~1 eV) are comparable to those measured by Packer and Skinner.2 1S. S. Pramana, T. Baikie, T. An, M. G. Tucker, J. Wu, M. K. Schreyer, F. Wei, R. D. Bayliss, C. L. Kloc, T. J. White, A. P. Horsfield, S. J. Skinner. J. Am. Chem. Soc., 2016, 138, 1273-1279. 2R. J. Packer and S. J. Skinner, Adv. Mater., 2010, 22, 1613-1616.

Resume : Acceptor doped BaZrO3 is well known for its high thermodynamic stability as well as high proton conductivity. It is therefore a promising candidate for applications in solid oxide fuel cells. In the last years it has been extensively studied with experimental and theoretical methods. These studies suffer from one problem, the obtained migration energies do not fit each other. In our work we present a new approach for the calculation of the ion conductivity. Starting from density functional theory (DFT) calculations we developed a conductivity model based on pair interactions with only a few parameters, which allows us to obtain ion conductivities and activation energies by using Kinetic Monte Carlo (KMC) methods. Every introduced parameter has been thoroughly analysed to gain knowledge on its influence on the ion conductivity. Using this model we investigate proton and oxygen vacancy conductivity in BaZrO3 including the investigation of different dopants and the role of percolation pathways. Our data are compared with theoretical and experimental values from literature and we are able to reproduce several trends. Through our model studies, we are able to get deeper insight into these phenomena.

Resume : As recently reported by Ming Li et al., A-site non-stoichiometry as well as B-site acceptor doping of Na0.5Bi0.5TiO3 (NBT) show a significant impact on the oxygen vacancy concentration and further the oxygen ionic conductivity [1, 2]. Mg acceptor doped NBT, for instance, shows an extremely high ionic conductivity comparable with conventionally used solid ion conductor materials. With respect to the experience with other lead based or lead free ferroelectric ceramics, this behavior was a rather unexpected result. The origin and defect chemical reasons for these findings are part of important ongoing research approaches. In this work, we will discuss the formation as well as the effect of oxygen vacancies in B-site acceptor doped Na0.5Bi0.5TiO3. With the help of temperature dependent impedance spectroscopy (IS) the defect chemistry and the charge carrier migration process is investigated. Furthermore, phase and charge carrier dependent simulations are included to get a deeper understanding of the origin for this unexpected conductivity behavior [3]. Based on these results we are able to propose how the investigated changes in NBT may affect other NBT related materials. References [1]. M. Li, M. J. Pietrowski, R. A. De Souza, H. Zhang, I. M. Reaney, S. N. Cook, J. A. Kilner, and D. C. Sinclair, Nat. Mater, 13, pp 31-35 (2014) [2] M. Li, H. Zhang, N. S. Cook, L. Li, J. A. Kilner, I. M Reaney, and D. C. Sinclair, Chem. Mater., 27, pp 629-634, (2015) [3] L. Koch, S. Steiner, K.-C. Meyer, I.-T. Seo, K. Albe, T. Frömling, J. Mater. Chem. C, 5, 8958-8965 (2017)

Resume : Acceptor doped ReBO4 (where Re is a rare earth element and B is Nb, Ta, As or Sb) are a group of chemically stable solid state proton conductors combining considerable proton conductivity, reaching 10-3 S/cm at 900 °C under wet conditions. Lanthanum niobate, the member of the group with highest ionic conductivity, undergoes a second order phase transition from tetragonal to monoclinic structure at about 500 °C, which is accompanied by an increase in the activation energy of the conductivity and a nearly twofold change of the thermal expansion coefficient (TEC). This challenge can be tackled by substituting Nb by different isovalent elements, such as As, Sb, Ta, and V to alter the phase transition temperature. This work summarizes the studies of the structure and electrical properties of solid solutions of LaNbO4-LaAsO4, LaNbO4-LaTaO4 and LaNbO4-LaSbO4. The structure of the samples has been determined by X-ray Diffraction method supported by Rietveld analysis. The electrical conductivity has been measured by Electrochemical Impedance Spectroscopy. Conductivity has been measured as a function of temperature, oxygen and water vapour partial pressure for the separation of the influence of different charge species on the total conductivity. The diffusion coefficient of oxygen ions has been determined by the isotope exchange method combined with Secondary Ion Mass Spectroscopy. This work was financially supported by the National Science Center, Poland Grant No. 2015/17/N/ST5/02813.

Resume : Last advances in the development of micro Solid Oxide Fuel Cells (?SOFC) have been connected with the downscaling of traditional SOFC functional layers to thin films, together with their integration in silicon technology. Classical restrictions of SOFC could be overcome, being able to lower the operating temperature to 400ºC. Despite such important leap, the technology encountered a new dilemma, since fast degradation was still found on the utilized metallic electrodes, but further lowering down was hindered by the internal resistance of the electrolyte. Operating at lower temperatures is desired, since it would not only allow a safe and stable use of metals, but would also facilitate an easier integration in real devices. For that, electrolyte materials with superior oxide-ion conduction need to be investigated. Here, we present the optimization of Bi2V0.9Cu0.1O5.35 (BICUVOX) as a thin film electrolyte for ?SOFC. Despite its high ionic conductivity, a poor chemical stability and low compatibility with other components of the cells have traditionally impeded its utilization in classical SOFC. However, the use of thin films and in a new low temperature range could solve the problem. A complete structural and electrochemical characterization of BICUVOX films deposited by pulsed laser deposition has been carried out, aiming to stabilize the high conducting aurivillus tetragonal phase. Best performing films showed the potential use of this material at temperatures as low as 250ºC.

Resume : The large impact of grain boundaries (GB) on the electrochemical behaviour of polycrystalline oxides materials has received increasing attention in the past decades. While for a large number of oxides GBs have been demonstrated to be detrimental for oxygen mass transport properties, recent studies showed that they produces a large enhancement of oxygen diffusion in Sr-doped Lanthanum Manganite (LSM) polycrystalline thin films. To understand and control the extraordinary properties of LSM GBs, we systematically investigated their chemical and structural composition in pulsed laser deposited polycrystalline thin films by High-resolution Transmission Electron Microscope (HR-TEM) and electron energy loss spectroscopy (EELS). The analysis revealed that a high density of dislocations occurs at the interface between the different oriented grains, along with a rearrangement of cationic composition. Also, the GBs show oxygen deficiency, which, in opposition to the typical hyper-stoichiometry presents in bulk LSM, appears to be the origin of the enhanced mass transport properties. We performed Density Functional Theory (DFT) calculations to investigate the formation energy of the cationic defects found in the GBs. The analysis revealed a strong intercorrelation among the various defects, helping to explain the local defect chemistry found by TEM. Finally, we analyzed the impact of the GBs local composition on electronic conduction, confronting polycrystalline and epitaxial thin films.

Resume : Understanding how the carrier mobility can be increased in oxides is one of the most significant challenges in order to obtain nanoelectronic based devices. The mobility of complex oxide is still orders of magnitude lower than that of semiconductors and with the current fabrication method we are still not fully able to control the carrier mobility at the interface. Here I will provide an overview of interface defects which influence the mobility at the interface observed in SrTiO3 (STO)-based heterostructures. I will also show that different scattering mechanisms at the 2D electron gas (2DEG) of SrTiO3-based interfaces can be controlled by defect engineering leading to enhanced mobility. Based on the enhanced mobility, in 2DEG samples of unprecedented structural perfection, we have recently studied the Quantum Hall Effect (QHE) which reveal the strength of enhancing the mobility. I will also show some results observed at these interfaces indicating a large positive magnetoresistance of 80,000% and the presence of a highly strain-tunable magnetic order. This collection of samples offers unique opportunities for a wide range of rich world of mesoscopic physics and future nanoelectronics.

Resume : Room temperature electron mobility of >130 cm2V-1s-1 is achieved for a few-layer MoS2 transistor by use of a polyanionic proton conductor as the top-gate dielectric of the device. The use of a proton conductor that inherently exhibits a cationic transport number close to 1 yields unipolar electron transport in the MoS2 channel. The high mobility value is attributed to the effective formation of an electric double layer by the proton conductor, which facilitates electron injection into the MoS2 channel, and to the effective screening of the charged impurities in the vicinity of the device channel. Through careful temperature-dependent transistor and capacitor measurements, we also confirm quenching of the phonon modes in the proton-conductor-gated MoS2 channel, which should also contribute to the achieved high mobility. These devices are then used to assemble a simple resistive-load inverter logic circuit, which can be switched at high frequencies above 1 kHz.

Resume : We demonstrated the fabrication of large-area ReS2 transistors and logic gates composed of a chemical vapor deposition (CVD)-grown multilayer ReS2 semiconductor channel and graphene electrodes. Single-layer graphene was used as the source/drain and coplanar gate electrodes. An ion gel with an ultrahigh capacitance e?ectively gated the ReS2 channel at a low voltage, below 2 V, through a coplanar gate. The contact resistance of the ion gel-gated ReS2 transistors with graphene electrodes decreased dramatically compared with the SiO2-devices prepared with Cr electrodes. The resulting transistors exhibited good device performances, including a maximum electron mobility of 0.9 cm2/(V s) and an on/o? current ratio exceeding 104. NMOS logic devices, such as NOT, NAND, and NOR gates, were assembled using the resulting transistors as a proof of concept demonstration of the applicability of the devices to complex logic circuits. The large-area synthesis of ReS2 semiconductors and graphene electrodes and their applications in logic devices open up new opportunities for realizing future ?exible electronics based on 2D nanomaterials.

Resume : Stoichiometric tantalum oxide (Ta2O5) dielectric films find wide applications in microelectronics due to their high dielectric constant, electrical strength and good thermal and chemical stability. For the last years, the interest in tantalum oxide has strongly increased due to its successful use in nonvolatile resistive random-access memories (ReRAM) or/and memristors. The optical and transport properties of non-stoichiometric tantalum oxide thin films grown by ion beam sputtering were investigated in order to understand the dominant charge transport mechanisms and reveal the traps nature. The TaOx films content was analyzed by X-ray photoelectron spectroscopy. From the optical absorption and photoluminescence measurements, and density functional theory simulations, it was concluded that the 2.75 eV blue luminescence excited in a TaOx films by 4.45 eV photons, originates from oxygen vacancies. These vacancies are also responsible for a TaOx conductivity. The thermal trap energy of 0.85 eV determined from the transport experiments coincides with half of the blue luminescence band Stokes shift. It is argued that the dominant charge transport mechanism in TaOx films is a phonon-assisted tunneling via traps. The exponential leakage current increase in TaOx with the decreasing x is explained by the increasing oxygen vacancy corresponding to a smaller distance between traps.

Resume : We report on the fabrication of solid-state photonic electrolytes based on cellulose nanocrystals (CNCs) and their integration into transistor devices. The CNC films with a left-handed internal long-range order are produced via evaporation induced self-assembly and consequently infiltrated with alkali ions (Li, Na and K) to yield highly polarizable chiral nematic electrolytes. The influence of anisotropy is studied through electrochemical impedance spectroscopy, yielding capacitances between 5 and 10 ?F cm-2. They are employed as gate dielectrics in electric double layer sputtered amorphous indium-gallium-zinc-oxide (a-IGZO) transistors. The obtained devices operate in depletion mode at low voltages (< 2 V), with On-Off ratios of up to 7 orders of magnitude, subthreshold swings of 77 mV dec-1 and saturation mobilities of 8.3 cm2 V-1 s-1. Anisotropic solid-state electrolytes based on abundant biopolymers show great potential for high performing cheap electronics. It is crucial to understand the fundamental transport mechanisms and their potential impact on technology, when compare to their isotropic counterparts. The developed films can find application in solid-state ionics for batteries, electrochemistry and microelectronic circuits.

Resume : Gadolinium-doped ceria (GDC) exhibits electrostriction that is comparable in magnitude to the field-induced strain of commercial, Pb-based electrostrictors. Given the ecological preference for ceria over Pb, we fabricated robust GDC self-supported MEMS in the form of millimeter-sized membranes, bridges, and cantilevers, using only Si-compatible processes and materials. We observed that the electrical contacts play a critical role in device functionality. Ti electrodes are the most suitable for active GDC membrane MEMS, as Ti contact resistance is lower than for Cr, Ni, Al and Ag electrodes. Measurements of membrane-displacement with atomic force microscopy and Michelson-Morley interferometry revealed a predominantly linear (1st harmonic) response to applied AC voltage (zero DC bias). We found that the amplitude of the 1st harmonic component is an exponentially increasing function of temperature with activation energy very similar to that for oxygen diffusion. Our results highlight a connection between electrostrictive strain and charge transport in GDC films. In the absence of electronic conduction, development of an electric field in the film depends on the mobility of oxygen vacancies, which renders the electro-mechanical properties more complex than in the case of classical electrostrictors. Funding by the Israeli MoS&T 3-12944 and 3-12421(collaboration with Russian Federation) and by the Russian Foundation for Basic Research (grant 15-52-06006 MNTI_?) are acknowledged.

Resume : Optical modulators are essential elements of photonic integrated circuits, where these devices are required for tuning, reconfiguration and stabilization operations. Different physical processes are used to manipulate the optical properties of a medium. In electrochromic materials, the optical behaviour is altered by electrochemical injection of ions and electrons. Applying an external voltage, the composition of the material changes, inducing a continuous variation of the optical properties. This mechanism could be exploited to realize an electrically driven optical modulator for photonic applications. To prove this concept we choose V2O5, a well-known cathode material for Li ion batteries [1], its layered structure can reversibly uptake/release a great amount of ions, and its optical properties are very sensitive to changes in stoichiometry. Adjusting the Li content in the V2O5 layers, the refractive index n and the extinction coefficient k shift [2]. This feature enables manipulating intensity and phase of light beams in very compact devices [3]. To implement this modulation in a photonic chip, a sputtered multi-layer stack is realized, where the ions reversibly travel from the Li-ion source to the V2O5 layer (battery principle) producing the desired change of the optical properties. [1] M. Winter et al., Adv. Mater. 10 (1998) 725. [2] M. Muñoz-Castro et al., J. Appl. Phys. 120 (2016) 135106. [3] S. Zanotto et al., Adv. Opt. Mater. 5 (2017) 1600732.

Resume : Surface and interfaces in electrochemical devices are key to the effective development of durable and efficient devices. Understanding the key processes such as oxygen reduction and incorporation, cation transport and segregation in oxide based devices is particularly challenging as both structure and chemistry have to be considered. In order to clearly elucidate the contributions at solid-solid and solid-gas interfaces a combination of techniques are required, and in this work we explore the interfaces in a model electrode system using primarily X-ray crystal truncation rod measurements as a function of operating conditions, and will highlight the power of this technique in exploring buried interfaces. This will be coupled with ion beam and X-ray spectroscopy measurements to provide a full picture of the atomic scale processes governing key mass transport phenomena.

Resume : Micro-solid oxide fuel cells (SOFC) can run with a broad variety of hydrocarbon fuels and feature low or even zero pollutant emissions, thus they can play a major role in the future portable power sources and can even act as sensors for the internet of things. Despite their potential, their applicability remains limited due to the high operating temperatures required for sufficiently high oxygen reduction and transport. In this work, we present a novel approach to develop epitaxial and mesoporous thin films with the aim to maximize the surface area of the films. Using pulsed laser deposition, we grew vertically aligned nanocomposites based on (La,Sr)(Co,Fe)O3 (LSCF) and different secondary phases. We optimize deposition parameters to obtain a two-phase composite with nanopillars between 20 nm and 100 nm. Selective etch-out of the nanopillars rendered mesoporous honeycomb-like nanostructures LSCF. It is demonstrated that by modifying the density and size of nanopillars, not only the nanostructure can be altered, but also it can be used as a strain engineering strategy to tune LSCF conductivity and catalytic activity. A thorough structural and functional characterization of the mesoporous materials will be presented to reveal synthesis-nanostructure properties. The results open a new route to develop nanostructured epitaxial mesoporous electrodes for micro-SOFC.

Resume : In this work, we focus on the oxygen electrode of solid oxide fuel cells where oxygen reduction occurs in two steps?adsorption and electronation, and surface/bulk diffusion to incorporation sites. Complex transition metal perovskite oxides such as strontium-doped lanthanum manganite (LSM) and strontium-doped cobalt iron oxide (LSCF) have been used as SOFC cathode materials. However both individually lack the key characteristics to successfully complete oxygen reduction. Furthermore, the accumulation of chromium (chromium poisoning) on SOFC cathodes is known to significantly hinder the performance of the cells. Incorporating core-shell hetero-structures as the cathode material could alleviate this problem: effectively combining the functionalities of both materials, and providing a nanoscale protection from Cr poisoning with a shell such as Cr-doped LSM (LSCM). However, synthesizing core-shell cathode structures previously has proved difficult requiring multiple steps, resulting in non-uniform core-shell structures. In this work, we utilize a molten salt synthesis process to synthesize core-shell structures with tailored length scales of the core and shell with great compositional control. The core is synthesized using any convenient processing method and added to a molten salt solvent. To this solvent, precursors of the shell forming materials added in calculated amounts. So long as the Gibbs free energy of formation of the target shell material from the precursors is sufficiently negative, the shell forms through a heterogeneous nucleation process around the core. The thickness and composition of the shell can be controlled by varying the process variables, namely precursor concentration in the solution, temperature, and time.

Resume : The nano-structured composite electrode, with a carefully conducted infiltration process, is one of the most promising electrode structures for intermediate temperature solid oxide fuel cells (IT-SOFCs), due to its promoted oxygen reduction reaction (ORR) and enlarged triple phase boundaries (TPBs). Among the various morphologies using infiltration, we reports an effect of film-coated cathode for IT-SOFCs with enhanced ORR kinetics and excellent stability. To facilitate the wet-chemical based film-coating technique, we controlled the fluid mechanical parameters when we prepared the precursor solution and pre-heating process of as-infiltrated samples. Following those approaches, we successfully deposited the target materials on the prepared scaffolds in a thickness of ~5 nm. Through the film-coating technique, we systematically designed the nano-structured Sm0.5Sr0.5CoO3-? (SSC)/Gd0.2Ce0.8O2-? (GDC) composite cathode. The film-coated SSC/GDC composite cathode showed the ~30% reduction in polarization resistance (Rp) and ~15% increase in peak power density at 650 °C compared to the conventionally coated cathode (discrete feature) in spite of ~12-fold less loading of infiltration materials. Furthermore, the film-coated cathode showed an excellent stability, maintaining an Rp of 0.029 ?cm2 for 100 h at 650 °C. Our results demonstrated that high performance and stability of the composite cathode for IT-SOFCs can be achieved through a thin-film coated cathode.

Resume : The high operating temperature (800?1000 ºC) of solid oxide fuel cells (SOFCs) has been a critical technical hindrance for broader applications because of a low chemical stability, slow start-up, and high system cost. At reduced temperatures, especially at low temperatures (< 500 ºC), the significant increases in SOFC components, in particular the polarization resistance of cathode, become critical as they often determine the entire SOFC performance. In particular, the oxygen reduction reactions (ORRs) at the cathode usually dominate the entire ionic transfer. Therefore, a high-performance cathode is crucial for the enhancement of SOFCs at low temperatures. In this study, we report a 3.5-fold improvement in the performance of SOFCs operating at 450 ºC with functional layer between the electrolyte and cathode, composed by electrospun yttria-stabilized zirconia (YSZ) nanofibers. YSZ nanofibers with diameters of 150-200 nm were uniformly deposited on single-crystal YSZ substrate. The dramatically enhanced polarization resistances were shown in electrochemical impedance spectroscopy, and that was caused by high specific surface, high porosity and nano-crystalline structure of the YSZ nanofiber functional layers. Our results show the possibility of applying YSZ nanofibers for the enhancement of high performance low temperature SOFCs.

Resume : Mixed-conducting perovskites with VO.., h. and OHO. are potential cathode materials for protonic ceramic fuel cells (PCFC). They incorporate protons either by hydration (water uptake, acid-base reaction for ) or hydrogenation (hydrogen uptake, redox reaction for )[1]. Thermogravimetry shows that the hydration degree is smaller for (Ba,Sr,La)(Fe,Co,Zn,Y)O3-? cathode materials compared to Ba(Ce,Zr,Y)O3-? electrolyte materials. The basicity of the oxide ions is identified as a key parameter for proton uptake, it is modified by the cation composition (substitution of Ba by Sr or La decreasing [OHO.], partial substitution of Fe by Zn increasing it). The maximum [OHO.] of 10% at 250 °C was found for (Ba0.95La0.05)(Fe0.8Zn0.2)O3-? [2]. The proton concentration of Ba-rich cathode materials is expected to allow for an extension of the reactive zone beyond the three-phase boundary. Quantitative analysis of oxygen stoichiometry and proton uptake shows a significant hole-hole and hole-proton interaction [3]. This non-ideality can be related to a partial delocalization of holes from the transition metal to the oxide ions, which affects also the protons by decreasing the oxide ion basicity. Quantitative modelling of this issue is discussed. Such interactions are key to understand the differences in cathode versus electrolyte materials proton uptake. [1] D. Poetzsch et al., Farad. Disc. 182 (2015) 129 [2] R. Zohourian et al., in preparation [3] R. Zohourian et al., ECS Transact, 77(10) (2017) 133

Resume : Fast oxygen surface exchange is of vital importance in solid oxide fuel or electrolysis cells and many studies investigated the dependence of its kinetics on external experimental parameters (temperature, partial pressure, applied voltage), sample geometry or microstructure (porosity, grain size, etc.), and sample composition. Also the exact surface chemistry and the strain state affect the oxygen exchange rate. Moreover, kinetic models have to include point defects, which themselves depend on external experimental parameters, composition, etc.. Owing to this complex situation, the oxygen exchange kinetics of oxides remains a strongly debated topic and novel experimental or theoretical approaches are essential for further progress. In this contribution, it is considered how some rarely investigated factors affect the oxygen exchange rates of oxides. i) The role of dislocations in Sr-doped LaMnO3 (LSM) thin films is discussed. ii) The relevance of defects on the oxygen exchange of (La,Sr)FeO3-x (LSF) is evaluated from I-V measurements. iii) Measurements on SrTiO3 (STO) upon UV illumination give further information on the role of electronic defects. iv) The dependence of oxygen exchange on the electrode thickness is investigated for (La,Sr)CoO3-x (LSC) films of 3-100 nm thickness. Here, a novel tool comes into play, in-situ impedance spectroscopy during pulsed laser deposition (I-PLD). v) The same tool allows a detailed analysis of kinetic changes caused by growth of hetero-layers. These I-PLD measurements also revealed existence of a still unknown factor modifying the oxygen exchange kinetics: Growing LSC films exhibit extraordinarily active surfaces with oxygen exchange resistances much lower than ever observed in ex-situ experiments.

Resume : Rare earth nickelates from the Ruddlesden-Popper (RP) series Lnn+1BnO3n+1 with Ln=La, Nd, Pr and B=Ni show exceptionally high oxygen diffusivities, high catalytic activity for oxygen reduction, and good electronic as well as ionic conductivities. Previous investigations on first order (n=1) RP-type rare earth nickelates demonstrated that the highest surface exchange rates are obtained for Pr2NiO4+? [1]. In the present study, the effect of partial substitution of Ni by Co in Pr2NiO4+? is investigated to further improve the surface oxygen exchange kinetics. In order to gain a deeper understanding of the oxygen exchange process in Pr2NiO4+? and Pr2Ni0.9Co0.1O4+?, dense thin film microelectrodes were prepared by pulsed laser deposition. The individual resistive and capacitive processes were investigated with electrochemical impedance spectroscopy as function of the oxygen partial pressure (1×10-3?pO2/bar?1) and temperature (550?T/°C?850). It was shown that B-site cation doping with small amounts of cobalt lowered the electrode resistance. The surface exchange coefficient kq calculated from the resistance of the electrode semicircle increased from kq = 2×10-7 cm s-1 for Pr2NiO4+? to kq = 5×10-8 cm s-1 for Pr2Ni0.9Co0.1O4+? at 850°C and 1×10-3 bar pO2. The observed exponents of the oxygen partial pressure dependence of kq are 0.73 for Pr2NiO4+? and 0.58 for Pr2Ni0.9Co0.1O4+? at 850°C. [1] C. Berger et al., Solid State Ion. 316 (2018) 93.

Resume : The perovskites structures? unmatched capability to accommodate virtually the whole periodic table of elements in the cation sublattice suggests the ability to tune the electronic and ionic defect structure towards favorable electrocatalytic activity by careful choice of the chemistry. Many favorable choices of chemistry, however, may lead to a departure from the ideal cubic perovskite structure, be it in the form of a complete decomposition or more subtly by ordering phenomena in either sublattice, impacting defect and electronic structure profoundly. One boiler plate example is the double perovskite PrxBa1-xCoO3-? (PBCO) where A-site as well as vacancy ordering may take place. In this work, we investigate the whole compositional space of PBCO in the form of active catalyst assemblies with sophisticated structural and spectroscopic methods to assay the phase relations and their impact on electronic and defect structure and with that the electrocatalytic activity. We find the anticipated transition from the hexagonal polytype in BaCoO3 to a cubic structure, and additionally the formation of superstructures along the substitution series, with the A-sites ordering at x = 0.6. These relations have profound impact on defect and electronic structure and surprisingly, aliovalent A-site substitution as well as the hexagonal to cubic transition only has a miniscule effect on the electrocatalytic efficiency, contrary to the A-site ordering showing a considerable one.

Resume : In depth understanding of the atomic processes taking place at the interface of catalyst and electrolyte is essential for optimizing catalytic properties of catalysts for electrochemical water splitting. This requires defined model systems that provide defined and tunable structural and electrical properties and, at the same time, possess electrochemical performance compatible with state-of-the-art compounds. Epitaxial thin films are one crucial way of generating thin films and surfaces with defined phase and crystallographic orientation as well as defined surface morphology and roughness. We discuss the structural and electrochemical properties of epitaxial cobaltite thin films, synthesized in growth-controlled phases involving cubic perovskites as well as oxygen-vacancy ordered double-perovskites. The electrochemical properties are shown to have little dependence on the bulk structure of the thin film, while electrical conductivity and cation stoichiometry seem to be key for increased catalytic performance. We compare (Pr0.5Ba0.5)CoO3?d and (La0.4Sr0.6)CoO3?d thin films and show that achievable current densities can be increased by one order of magnitude (>150mA/cm2) by changing the cation composition, while maintaining atomically defined step terrace structure.

Resume : Motivated by the recent realization of cluster-assembled nanomaterials as gas sensors, first-principles calculations are carried out to explore the stability and electronic properties of cluster-assembled nanowires based on X12Y12 (X=Zn, Ga, Al, Y=O, N) clusters cluster-assembled nanowires and the adsorption behaviors of environmental gases on the X12Y12-based nanowires. Our results indicate that the ultrathin X12Y12 cluster-assembled nanowires have semiconducting electrical properties with direct energy gaps, and are particularly thermodynamic stable at room temperature. By analyzing the adsorption energy, adsorption types (chemisorption or physisorption), charge transfer, the adsorption behavior of the target molecules comparison with other common molecules, the change of electronic properties (particularly, DOS, band structures, and electric conductivity), the recovery time before and after the adsorption, we can confirm that the Zn12O12-based nanowire is a potential candidate for gas sensors with high sensitivity and selectivity for NO and NO2 detection, and the Al12N12-based nanowire should be a highly sensitive CO and NO sensor with quick response as well as short recovery time, and the Ga12N12-based nanowire should be a promising gas sensor for CO, NO, and NO2 detection.

Resume : Here we present the phase diagram of \ce{Ce$_{1-x}$Gd$_{x}$O$_{2-x/2}$} (CGO), calculated by means of a combined Density Functional Theory (DFT), cluster expansion and lattice Monte Calro approach. Methodology is well tested in the whole range of concentrations ($x \equiv x_{\ce{Gd}} \leq 1$) and is reliable. In the thermodynamic equilibrium, we observe two transitions ($x_{\ce{Gd}}\gtrsim0.3$): an onset of oxygen-vacancy (\ce{O-Va}) ordering at \emph{ca.} 1300K--3300K ($x_{\ce{Gd}} = 0.3\text{--}1$), and then, below \emph{ca.} 1000 K, a phase separation into \ce{CeO2} and C-type \ce{Gd2O3} ($x_{\ce{Gd}} = 0\text{--}1$). We also model quenched systems, with cations immobile below 1500 K, and observe that immobilised cations does not prevent the C-type order. The boundary between C-type \ce{Va} ordered and fluorite solid solutions is found to be $x_{\ce{Gd}} \approx 0.27$. For smaller concentrations \ce{O-Va} sublattice freeze into a random-like state upon cooling. Transition temperatures for \ce{Va} ordering (thermodynamic and quenched) compare well with existing experimental data. Moreover, DFT calculations of quenched structures show that \ce{Va} ordering affects lattice parameter and relaxation of cations, in good accordance with recent experimental findings. We also estimate the effect of ordering and composition on cations' misorientation from ideal C-type structure. The effect of ordering on ionic conductivity is discussed. Altogether, current study provides a deep understanding of structure and ordering in CGO consistent with the body of experimental data and allows to rationalise it.

Resume : Strontium titanate, SrTiO3, is a wide band gap electroceramic that belongs to the most investigated perovskites. By introducing iron on the structural B site a perovskite-type solid solution is formed over the entire composition range from SrTiO3 to SrFeO3. The SrTi1-xFexO3-? system can be used in a variety of important applications such as oxygen permeation membranes, solid oxide fuel cell electrodes, oxygen sensors or as the switching oxide in resistive random access memories. Despite extensive studies on the mixed ionic-electronic conduction and oxygen exchange kinetics of SrTi1-xFexO3-? [1],[2], Raman spectroscopic studies are scarce in this system [3]. However, Raman can be a powerful tool to obtain information on local atomic arrangements in relation to the defect chemistry by correlating the spectra with the materials stoichiometry and composition. Here we firstly review insights on Raman spectra, defect chemistry and structural symmetry for the SrTi1-xFexO3-? solid solution system over the whole composition range in thin films and pellets. Secondly we interpret the Raman spectra as a function of the stoichiometry and composition. The experiments are carried out using an electrochemical cell where the stoichiometry can be controlled by an applied bias. The intensity and position of the Raman peaks associated to the oxygen vibrations around the iron are linked to the local atomic arrangements. These findings introduce a controlled method of probing oxygen vibration modes with Raman spectroscopy as a function of the materials stoichiometry, which can be applied to various functional oxide materials helping Raman spectra interpretation but also probing materials properties on the near order. In this way we highlight the importance of Raman spectroscopy to understand and probe defects in functional oxides and present a precursor for Raman in-operando experiments on the device level. 1. A. Rothschild, W. Menesklou, H. L. Tuller, and E. Ivers-Tiffe, Chemistry of Materials, 18, 2006. ? 2. W. Jung and H. L. Tuller, Advanced Energy Materials, 1, 2011. ? 3. M. Vracar, A. Kuzmin, R. Merkle, J. Purans, E. A. Kotomin, J. Maier, and O. Mathon, Physical Review B, 76, 2007. ?

Resume : Doped ceria is of major technological interest in energy related applications like solid oxide fuel cells, solid state batteries, and the production of solar fuels. The presence of defects, their interactions and their mobility determine key properties of the material. Density functional theory (DFT) calculations can provide information about defect energies on the atomic scale while Monte Carlo (MC) simulations are able to predict properties like phase stability and conductivity. Combining both methods enables the prediction of macroscopic quantities from first principles calculations. In this talk an overview of our recent computational research on bulk properties of doped ceria is presented. This includes the calculation of the energies of migration for oxygen ions in different dopant environments as well as the mutual interaction of defects. In addition to the energies the influence of vibrational entropies to defect formation, interaction and migration are considered. Monte Carlo simulations based on the first principles results are conducted to predict the distribution of defects, their influence on the redox behaviour and the ionic conductivity. The calculations reveal a strong influence of the atomic scale defect interactions on the macroscopic properties. These interactions can explain the dependence of the ionic conductivity of doped ceria on the type of dopant and doping level due to trapping of oxygen vacancies by the dopant ions and blocking of the migration path. In addition, defect interactions are responsible for the increased reducibility of Gd or even Zr doped ceria compared to pure ceria. Our results underline the importance of the interactions between individual defects on macroscopic properties.

Resume : Oxygen diffusion in acceptor-doped ceria, in which oxygen vacancies are responsible for diffusion, has been studied extensively. In contrast, the diffusion of oxygen in donor-doped ceria, in which oxygen interstitials are the dominant oxygen defects, has received little attention. In this study, we synthesised and characterised ceramic samples of CeO2 doped with 1 mol % Nb2O5. Two different experimental methods were used to probe the diffusion of oxygen. 1) 18O isotope exchange experiments with subsequently analysis by means of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) were conducted. From these measurements, the tracer diffusion coefficient of oxygen was determined. The exchange experiments were conducted in a temperature range from 773 K to 973 K and with an oxygen partial pressure of 0.2 bar. 2) Electrical Conductivity Relaxation experiments, in the Van der Pauw, configuration, were carried out, at different temperatures ranging from 873 K to 1073 K and oxygen partial pressure ranging from 10-6 to 10-1 bar. From the relaxation curves the chemical diffusion coefficient of oxygen was determined. With the thermodynamic factor calculated from defect calculations, chemical diffusion coefficients were transformed into tracer diffusion coefficients, and these data compared with results from the isotope exchange experiments. The results show a similar temperature dependent behaviour for both experiments, with an activation enthalpy of oxygen tracer diffusion roughly 0.8 eV.

Resume : In oxygen transport membranes (OTM), the dense ceramic separation layer is a fundamental component and is intended to produce oxygen with high selectivity. To function with high efficiency, both high electronic and ionic conductivity are required as well as high stability and long durability over a wide range of oxygen partial pressure. Recently accumulated attention has been focused on exploring dual-phase composite materials in order to fulfil the requirements. Among all the essential criteria, transport properties are profoundly important aspects. The experimental techniques used to determine the oxygen transport kinetics in this work were Isotopic Exchange Depth Profiling (IEDP) and Secondary Ion Mass Spectrometry (SIMS) [1] combined with Low Energy Ion Scattering (LEIS) to investigate the surface behaviour of the materials. In this work the Lanthanum Strontium Chromium Ferrite (LSCrF)-Scandium Stabilised Zirconia (ScSZ) based dual-phase materials have been investigated. Diffusion measurements were firstly carried out at the macroscopic scale and the ?effective? diffusion kinetics were obtained. In order to achieve the optimal properties, variations on different compositions and microstructures have been carried out. Whilst the OTM can function effectively with the LSCrF-ScSZ composite materials, the detailed mechanism by which the dense layer transports oxygen is unclear and the investigations on the oxygen diffusion mechanisms of the dual-phase composites are extremely limited. In oxygen diffusion studies at the microscopic scale using Focused Ion Beam (FIB)-SIMS, a synergistic effect between the two phases was observed in the composite materials: a decreased surface exchange coefficient (k) was observed for the mixed ionic and electronic conducting (MIEC) phase LSCrF while an enhanced k was obtained for the pure ionic conductor (ScSZ) compared to their corresponding isolated single-phase materials. Subsequently, the mechanism studies of the oxygen transport in the composites were performed on a specialised sample by applying IEDP, SIMS and LEIS techniques in order to study the different hypotheses in literature for the oxygen transport mechanisms of the dual-phase composite materials, i.e. cation inter-diffusion, spillover and self-cleaning effects. References [1] J. A. Kilner et al., Journal of Solid State Electrochemistry, 15 (2011) 861-876.

Resume : Materials with layered Ruddlesden?Popper structure having high oxygen mobility are promising for SOFC cathodes and oxygen separation membranes. This work aims at studying structural and transport features of Pr2-xCaxNiO4+? (x=0?0.6) synthesized by co-precipitation method and sintered at 1200 °C. Samples were characterized by in situ XRD using synchrotron radiation, TGA, oxygen heteroexchange with C18O2 and impedance spectroscopy. For Pr2NiO4+? a reversible Fmmm?I4/mmm phase transition occurs at ~480°C in air in agreement with TGA data, while for some doped samples irreversible I4/mmm?Fmmm phase transition occurs in Ar. Doping by Ca decreases the interstitial oxygen content in PCNO and, hence, the oxygen self-diffusion coefficient by 2 orders of magnitude up to x=0.3. At higher Ca content three channels of fast, slow and very slow oxygen diffusion with typical D* values being ~ 10-11, ~ 10-13 and ~ 10-16 ? 10-14 cm2/s at 430 °C were revealed corresponding to cooperative mechanism of migration, hampered cooperative migration in near-dopant positions and migration via vacancy mechanism in perovskite layers, respectively. The ionic conductivity remains rather high (~10-3?10-1 S/cm) being attractive for the practical application. Total conductivity varies non-monotonously with Ca content in the range of 60 -130 S/cm at 700°C reaching a maximum at x=0.5. Support by Russian Science Foundation (Project 16-13-00112) is gratefully acknowledged.