Solid state ionics: thin films for energy and information applications

Resume : With planar NAND Flash memory technologies approaching its physical limits, the semiconductor memory industry is looking into non-silicon alternatives with the potential to compete with and eventually replace the main stream technology. Over the last decade several memory technologies based on a resistance change effect, commonly referred to as resistive RAM, have been developed. Prominent examples are Magnetic RAM (MRAM, STT-MRAM), Phase Change Memory (PCM), Conductive Bridge Memory (CBRAM), and oxide based RRAM. Oxide based RRAM cells comprise of one or more functional oxide layers. The resistance change is based on an electric field driven redistribution of oxygen vacancies within the layers causing a variation of the electrical conductivity. Even though there are similarities in the operation compared to solid oxide fuel cells and batteries, high electric fields, self-heating, interface effects, and the lack of knowledge of the material properties on the nanoscale are key challenges in indentifying underlying mechanisms and improving the performance of oxide RRAM devices. The tunnel RRAM is one example of an oxide based RRAM. The device is formed by a two layer structure comprising of a thin ZrO2 tunnel oxide layer and a conductive perovskite layer, which is typically a manganate. The tunnel RRAM is characterized by a uniform rather than a local change in conductivity, which allows describing the behavior using 1D models. The resistive memory effect is achieved by exchanging oxygen vacancies between the conductive layer and the tunnel barrier. In the presentation, we will review the device functionality and the current state of understanding of the device physics. Opportunities and challenges regarding device modeling and optimization as well as requirements for emerging memory technologies to be able to make the transition from lab to product will be discussed.

Resume : Ionic and electronic transport in functional oxide materials is of great relevance for applications in the fields of energy and data storage, e.g. solid oxide fuel cells (oxygen ion conductivity), oxygen permeation membranes (ambipolar diffusion of oxygen), or data storage materials (electronic and/or ionic conductivity). In this contribution our recent work on highly non-stoichiometric thin film oxides will be discussed with special emphasis on amorphous, highly non-stoichiometric oxides. In amorphous solids structural disorder can lead to an insulator–metal transition on account of Anderson localization, i.e. the electronic states below the mobility edge are localized. If the Fermi energy passes through the mobility edge the material changes from an electronic insulator to a metal. In addition, large deviations from the ideal stoichiometry of an oxide, that is, high defect concentrations, provide a high concentration of electronic defects (self-doping). We will consider examples of highly disordered oxides that were prepared by pulsed laser deposition and discuss their electronic conductivities and their application in resistive memory devices.

Resume : Although there exists a general consensus that bipolar resistive switching in transition metal oxides is in most cases connected with a redox-process, the details of the underlying physical mechanism are only poorly understood up to now. One of the obstacles for its further elucidation is that the net changes of structure, stoichiometry and valence state during electroforming and switching are very small and occur primarily at the electrode interface ore within nanoscale filaments. In this talk, we will present an overview over the current state of experimental verification of the proposed switching models. For epitaxial SrTiO3 thin film devices, by the combination of scanning force microscopy with photoelectron spectromicroscopy and X-ray absorption spectroscopy, we were able to prove that electroforming goes along with a homogeneous as well a local formation of oxygen vacancies. Moreover, significant changes are detected in the chemical state as well as in the relative stoichiometry of the cation sublattice during electroforming demonstrating the formation of new phases. By performing hard X-ray photoelectron spectroscopy, we could experimentally prove that resistive switching in Pt/Ti/PCMO/SRO/STO devices is based on a redox-process, which mainly happens on the Ti side. The different resistance states are determined by to the amount of fully oxidized Ti-ions in the stack, implying a reversible redox-reaction at the interface, that governs the formation and shortening of an insulating tunnel barrier.

Resume : In most resistive switching (RS) devices, the commutation of resistance among diverse states is explained in terms of formation and rupture of conductive filaments (CFs) made of ionic species inside a Metal-Oxide-Metal stack. The filamentary-type of operation leads to important implications for downscaling capabilities as well as for operation variability, reasons why a clear understanding of the evolution of the CF shape during formation and rupture processes is a decisive issue. In the present work the tip of a Conductive Atomic Force Microscopy (CAFM) is employed as a mobile electrode on a HfO2/TiN RS structure. First we recognize that in the initial state the conduction is localized in nanometric paths activated by defects sited near the HfO2/TiN interface. The defective paths develop into CFs when a sufficiently high voltage is applied to the structure, reducing the resistance of a RS device. We demonstrate that CFs can be disrupted, closing a RS cycle and restoring a high resistance state. The AFM tip is also used to address single CFs and to study how the operation over one filament influences the neighboring ones. Finally we propose a comprehensive picture of the evolution of CF shape during formation and rupture: rather than a group of nearly parallel and independent CFs, a network of conductive branches ramifies from the defects that activate the conduction in the initial state. This work is partially supported by Fondazione Cariplo (MORE Project n?2009-2711).

Resume : Ionic currents determine the functionality of various devices for energy and information applications, such as Li-ion batteries, fuel cells, or memristor-type applications. To understand device limitations and to draw a roadmap to optimize device properties, the ionic flow has to be studied on relevant length scales of grain sizes, structural defects, and local inhomogeneities, i.e. over tens of nanometers. Knowledge of the interplay between the ionic flow, material properties, and microstructure can be used to optimize the device properties, for example to maximize energy density, increase charging/discharging rates, and improve cycling life for Li-ion batteries for applications in electric vehicles and aerospace. Scanning Probe Microscopy (SPM) is a universal tool to study electromechanical effects in oxide materials. While used extensively to investigate the piezoelectric effect in ferroelectric materials, SPM was used in various ways to study ionic transport in oxides in recent years. Ionic transport in these systems can be studied through the interplay of materials volume changes and ionic concentration and the interaction of near-surface charges and the SPM tip. In this talk, we want to give an overview over what has been achieved in the fields of Li-ion batteries, Li-air batteries, fuel cells, and electrochemical supercapacitors using SPM-based techniques. We will focus on SPM signal generation and data interpretation and provide numerical and analytical models to support various scenarios. The goal is to show the possibilities of SPM-based methods to study ionic transport in various material systems with an unmatched lateral resolution and highlight the interplay between ionic transport and microstructure. Support was provided by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division, Scientific User Facilities Division, and by the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center.

Resume : Enhancement of ionic conductivity in thin films or multilayers of oxide materials, i.e. doped zirconia and ceria, has sparked great interest in the search for fast ion conducting structures for fuel cells as well as for red-ox based resistive memories. The enhancement in ionic conductivity in such structures could be attributed to elastic strain arising from the lattice mismatch at the interface. However, this assumes that the interface between two materials is perfectly coherent, while in most cases dislocations are observed, and these dislocations relax the interfacial elastic strain. The strain field and the electrostatic field that arises from the dislocations can also impact the defect stability, distribution and mobility in these materials; and yet, the role of dislocation on the ionic conductivity is not consistently reported in the literature nor is it clearly understood. The aim of our work is to quantitatively assess the dislocation's influence on the ionic conductivity in fluorite and perovskite oxides, exemplified by doped CeO2 and SrTiO3, respectively. Edge dislocations in in these materials are studied by atomistic simulations combining the Monte Carlo, Molecular Dynamics and Nudge Elastic Band calculations. Asymmetric distribution profiles of dopant cations and oxygen vacancies are found as a result of the strain field of the dislocation, and the diffusion kinetics along and across the dislocations is found to depend on the structure and composition.

Resume : Among advanced materials for clean energy, oxygen-deficient mixed conducting perovskites BSCF and LSCF are considered as promising materials for cathodes in solid oxide fuel cells (SOFC) and oxygen permeation membranes. BSCF exhibits the best oxygen exchange performance amongst similar materials, which can be related to its mixed electronic and ionic conductivity. In particular, its high oxygen vacancy concentration and low diffusion activation barrier contribute to the fast oxygen reduction kinetics. However, it exhibits a tendency to decompose at intermediate temperatures into a mixture of cubic and hexagonal perovskite phases which is detrimental for its use. In order to understand a mechanism of this unwanted process, first principles quantum mechanical calculations of BSCF and LSCF with different oxygen deficiency were performed and possible decomposition scenarios studied. It was shown that formation energies of oxygen vacancies in the cubic and hexagonal phases of BSCF differ considerably not only in absolute values, but also in their variation with the actual oxygen non-stoichiometry. In fact, it is a large oxygen non-stoichiometry that makes the cubic phase more stable than the hexagonal one. LSCF is shown to be much more stable with respect to such a phase transformation. The first principles calculations are accompanied with the thermodynamic analysis of the conditions under which the cubic phase is stable. M. Kuklja, E.Kotomin, R. Merkle, PCCP 15, 5443 (2013).

Resume : Ionic conduction and diffusion in micro-/nanoscaled materials differs significantly from bulk materials. This is due to the modified transport properties of solid-solid interfaces and surfaces. In this contribution a literature overview is given on experimental studies treating ionic transport in thin films and multilayers. By reviewing and comparing the data, the magnitudes of the observed interface effects can be classified, considering the total increase of the conductivity/diffusivity together with the layer thickness. The least effect can be found i) in case of transport along boundaries between extrinsic ionic conductors (and insulator). Mediocre effects can be measured for ii) transport along surfaces of extrinsic ionic conductors. The highest effects are reported for iii) transport along boundaries between intrinsic ionic conductors. The effects differ by about two orders of magnitude (1 : 101 : 102). The modified interface transport in category i) is most probably due to strain effects, misfit dislocations or disordered transition regions. Focussing on strain effects, an analytical model, based on a phenomenological description will be presented. A multilayer consisting of crystalline thin films with coherent interfaces and biaxial mechanical strain due to lattice misfit is assumed. The conjoined layers consist of columnar crystallites with constricted cross section, enabling strain relaxation by shear. Expressions for the total ionic transport relative to bulk transport and for the spatial extent of the strained interface regions as a function of the layer thickness are obtained. The model is used to describe experimental data from O2- conductivity and 18O diffusion studies as well as from XRD strain studies, performed on YSZ/rare earth metal oxide multilayers with systematically varied lattice misfit.

Resume : The role of defects is a focus of the ongoing discussion about the electronic properties of the conducting interface between the two insulators LaAlO3 (LAO) and SrTiO3 (STO). In this study, the LAO/STO-interface is discussed from a defect chemical point of view. Utilizing conductance measurements in high temperature equilibrium with the surrounding atmosphere we discuss the conduction mechanism and defect-related charge compensation mechanisms at the LAO/STO interface. In particular, we will show that at high oxygen partial pressures Sr-vacancies are formed as a result of an unavoidable thermodynamic equilibrium process (Schottky-equilibrium). These acceptor-type defects reduce the electron density finally resulting in insulating interfaces. We furthermore investigated the transport properties of LAO/STO-bilayers. The interplay of cationic defects in the STO layer and electronic properties of the bilayer-interface is systematically analyzed by a growth-controlled variation of the cation-stoichiometry in the STO thin films. Resistance measurements and Hall measurements on various bilayer-samples reveal a stoichiometry-effect on both electron mobility and carrier density. The results indicate an enhancement of scattering processes in as-grown non-stoichiometric samples which is in line with an increased density of defects.

Resume : To get autonomous smart microsystem, a miniaturized power source should be integrated. As the device is surface limited, the energy and power performances of commercially available planar microbatteries and micro-supercapacitors are not sufficient to reach this goal. To improve their performances while keeping constant the footprint area of such devices, a 3D topology is proposed. The silicon micropillars and microtubes fabricated by a top down approach allows to reach a high area enlargement factor (AEF). Energy density can be increased by one or two orders of magnitude compared to standard planar micro-devices, thus providing improved autonomy to the powered microsytems. Step conformal deposition of platinum (current collector) and TiO2 (negative electrode of the Li-ion microbattery) are performed on the 3D structures by Atomic Layer Deposition facility. With a 3D scaffold having an AEF close to 25 combined with a 150 nm thick TiO2, a surface capacity of 0.2 mAh/cm2 at C/10 is reported. A micro-supercapacitor electrode based on a thin manganese dioxide film is conformably grown by pulsed electrodeposition on the 3D topologies. A MnO2 film (275 nm thick) reaches 250 mF/cm? at 5 mV/s. The surface capacitance is drastically enhanced compared to a standard 2D electrode with a comparable thickness. This study shows promising AEF leading to high energy density while keeping enough spacing in the microstuctrures array to allow the deposition of the overlying layers.

Resume : Cation segregation to the surface of materials for SOFC applications is known to impact on overall device performance and hence is of great interest both fundamentally and practically. Experimental studies focused on the transport properties of ion conductors when grown as strained thin films have recently attracted considerable interest, yet cation segregation is rarely considered. However, changes in the chemical composition cannot be neglected especially when the dimensions of the films approach those distances (tens of nanometers) over which cation segregation is expected to occur. In this work we have employed Low Energy Ion Scattering (LEIS) to study the (100) surface of CGO films on STO, YSZ and LAO substrates and the (111) surface grown on sapphire fabricated by pulsed laser deposition (PLD). We show that as-grown films show minimal segregation despite high temperatures used during fabrication (600 - 800?C), yet the surface composition varies drastically from the nominal bulk when heated post growth to temperatures associated with processing or conductivity measurements (800 - 1000?C). Furthermore we find that the strain induced on the films by the substrates, as measured by XRD, affects the extent of the surface segregation. After an 800?C anneal CGO films grown on STO are observed to have a surface Gd/Ce ratio of over 7 times that of the bulk composition whereas those grown on LAO show only a three-fold increase, with the CGO/YSZ system being the intermediate case. The effects of lattice strain on the driving force for dopant segregation will be discussed along with the composition profile as the film thicknesses are decreased to the length scales associated with the segregation effects.

Resume : During the last 10 years, the quest for a replacement gate dielectric in field effect transistors has been a powerful driver to investigate the deposition of ultra thin oxide thin films. Replacing SiO2 with HfO2 in transistors was a major breakthrough for the microelectronic industry and generated a lot of know-how. This knowledge is today cross-fertilizing research areas that are not limited to the search for a new gate dielectric. Controlling the interface between the oxide and silicon has for example always been a key issue. This specific research triggered the development of new deposition processes, enabling researchers to grow high quality, crystalline, complex oxide films onto silicon. Such “functional” oxides have physical properties that make them very attractive to perform functions that will be required in future Information and Communication Systems. Properties such as ferroelectricity, piezoelectricity or electro-optic activity is often tightly depending on the ionic character of these materials, on the structural details in the cationic or anionic sub lattice, etc. This presentation will deal with the opportunities and challenges to combine silicon microfabrication techniques with the capability to grow crystalline directly on silicon. It will in particular focus on the use of ferroelectric perovskites for photonic circuits in future systems, and how defect chemistries might play a crucial role.

Resume : In surface science ceria is a highly interesting material owing to its attractive catalytic surface activity and it was thus intensively investigated within the last decade. This high catalytic activity was recently demonstrated to be also very beneficial for the electrochemical H2 oxidation on Sm doped CeO2 electrodes with noble metal current collectors [1]. For further improvement and understanding, analysis of the effect of (co-)doping on transport and surface kinetics is helpful. In the present study, model-type thin films of Gd doped and Gd/Mn co-doped ceria were investigated by means of impedance spectroscopy in humid H2 atmosphere. A novel measurement technique for microelectrodes with interdigitating Pt current collectors was employed. This method allows a separation of the different elementary processes contributing to the electrode impedance. After annealing at 650 °C in humid H2 atmosphere, the electronic conductivity of Gd-doped ceria is higher than that of the co-doped material. In terms of surface exchange rate, however, the Gd/Mn co-doped ceria shows the higher activity. In addition 18O tracer incorporation into Gd-doped ceria electrodes from a H2/H218O atmosphere was performed with and without cathodic polarization. The tracer distribution within the ceria thin film was subsequently analyzed by secondary ion mass spectrometry (SIMS) and correlated with the electrochemical results. [1] Chueh et al. Nat. Mat. 11 (2012), p.155

Resume : For high-temperature energy applications, e.g., as solid oxide fuel cell cathodes or as dense ceramic oxygen-permeation membranes, mixed ionic-electronic conducting (MIEC) perovskites, namely of the composition (AxSr1-x)(CoyFe1-y)O3-delta (A = La, Ba, Pr), are promising candidates given their excellent oxygen-ionic and electronic transport properties. A high level of oxygen non-stoichiometry is an important prerequisite for a high performance; however, the structural stability of the oxide is also affected by oxygen deficiency. Changes in oxygen stoichiometry Δdelta were determined by coulometric titration experiments performed on selected state-of-the-art MIEC samples (BSCF, LSCF, PSCF) in a tubular zirconia “oxygen pump” setup. This setup facilitates precise oxygen partial pressure control in the entire range between pO2 = 10^-18 ... 1 bar between 700 °C and 900 °C. By monitoring the electric current necessary for pumping oxygen through the solid electrolyte into or out of the measurement chamber, the amount of oxygen transported and, thus, changes in oxygen stoichiometry can be determined with a high resolution. All experiments were performed on fine-grained powders to avoid kinetic influences resulting from non-equilibrium conditions. The Δdelta(pO2) behaviour was investigated for the above-mentioned high-performance MIEC oxides down to their low-pO2 stability limits which were similar for all compositions (< 10^-10 bar at temperatures of 700…900 °C).

Resume : The kinetics of oxygen transport is essential for an application of mixed ionic-electronic conducting (MIEC) oxides as solid oxide fuel cell (SOFC) cathodes, as high-temperature gas sensors or as oxygen-permeation membranes. The performance of the materials is determined by the chemical diffusion coefficient D and the surface exchange coefficient k. Commonly, D and k values are determined by electrical conductivity σ relaxation (ECR) using different gas mixtures. Here, however, a closed tubular zirconia “oxygen pump” [1] was used which facilitates precise control of oxygen partial pressure pO2 continuously within the entire range between 10^-18...1 bar at temperatures above 700 °C to determine D and k values for several MIEC oxides such as BSCF and LSCF [2]. In this study we evaluate D and k values by numerical analysis (using MATLAB) of both pO2(t) and σ(t) with the focus on the influence of sample response behaviour, sample geometry, amplitude of pO2 steps (in the range from 10^-5...10^-1 bar), and setup-dependent flush times on the determinability and accuracy. This analysis tool was developed in order to identify a confidence region for (ideally) a set of both D and k values or (in the case of diffusion control) only a D value or (for surface control) only a k value. References [1] C. Niedrig et al., J. Electrochem. Soc. 160, F135 (2013) [2] C. Niedrig, H. J. M. Bouwmeester et al., manuscript in preparation

Resume : A high-temperature measurement setup was developed to deconvolute the electronic conductivity in mixed ionic-electronic conducting (MIEC) oxides at temperatures as high as 600 °C. We focus on (Ba0.5Sr0.5)(Co0.8Fe0.2)O3-δ (BSCF) which is a very promising candidate for an application as oxygen-permeation membranes due to its excellent permeation properties [1]. Its conductivity mechanism as a function of temperature has, however, so far not been fully understood. Determination of the (p-type) electronic carrier concentration and mobility may contribute to this understanding. The very low Hall mobilities require frequency-selective measurements which we realized by lock-in technique. The setup includes an alumina high-temperature sample holder with which a 5-point contacted homogeneous sample can be inserted into an external magnetic field of variable flux density B (up to 700 mT), resulting in a Hall voltage perpendicular to both B and the electrical current I. Additionally, a sealed setup enables measurements in different gas atmospheres [2]. By using BSCF thin-film samples chemically deposited onto NdGaO3 single-crystalline substrates [3] a satisfactory signal-to-noise ratio is ensured for the Hall voltage. References [1] J. Sunarso et al., J. Membrane Sci. 320,13 (2008) [2] R. Moos, W. Menesklou, K.H. Härdtl, Appl. Phys. A 61, 389 (1995) [3] K. Asano et al., Solid State Ionics (2013), submitted

Resume : Bismuth oxide has seen interest as a material for solid oxide fuel cells, since it is an ionic conductor, i.e. oxygen atoms move through it. Herein, we present results on bismuth oxide thin films grown by pulsed laser deposition and radiofrequency-assisted pulsed laser deposition, in oxygen atmosphere. The influence of the deposition parameters, i.e. laser wavelength, fluence, oxygen pressure, the use of an oxygen plasma, and substrate type and temperature, on the thin film structure and morphology, are discussed. A comparative study is presented here, on the advantages of using laser processing and micro-/nano structuring vs. other techniques, for applications in solid oxide fuel cells.

Resume : Li doped spinel, Ni1-xLixCo2O4, thin films were fabricated by sputtering and pulsed laser deposition. Thin films were grown on glass and c-sapphire single crystal substrates at various substrate temperatures and oxygen partial pressures. The effects of the processing parameters on the crystal structure, electrical and optical properties of Li- doped spinel thin films were analyzed by XRD, AFM, four point probe method, and UV spectrometer. As the doping concentration x increased, the electrical conductivity increased up to x=0.3. The optical transmittances increased with increasing substrate temperature up to 400℃. The thin films growth with strong (111) preferred orientations were observed on the sapphire substrates. Li doped Ni1-xLixCo2O4 spinel thin films with electrical conductivity of 60 S/cm and optical transmittance about 50% were fabricated with optimum processing parameters.

Resume : We report on the effects of substrate temperature (Ts) on the morphology and structural properties of Hydrogenated nanocrystalline silicon (nc-Si:H) thin films, grown by radio frequency Plasma Enhanced Chemical Vapor Deposition (PECVD) on silicon single crystal (1.0 0) using a gas mixture of silane (SiH4) and hydrogen (H2). Substrate temperature was varied from room temperature to 450 °C. Characterization of these films X-ray diffraction (XRD), Raman spectroscopy revealed that the crystallite size and at same time the volume fraction of crystallites in the films tends to decrease with increase in Ts. The Fourier transform infrared spectroscopic analysis (FTIR) showed at low temperature the hydrogen is incorporated in the nc-Si:H films in the mono-hydrogen (Si-H) bonding configuration. With increasing Ts the hydrogen bonding in nc-Si:H films shifts from mono-hydrogen (Si-H) to di-hydrogen (Si-H2) and (Si-H2)n. The hydrogen content in the nc-Si:H films decreases with increase in Ts. From The Atomic Force Microscopy (AFM), it was shown that the increase in Ts tends to increase the porosity and decrease the crystalline grain size. In order to more understand the effect of Ts on this structural change, Minority Carrier Lifetime (MCL) measurement show that only the films with a nanocrystalline silicon structure present an enhancement in MCL which could be related to a quantum size effect and to the SiH-related bonds

Resume : The use of UV steady state illumination increases the spectral sensitivity of a double pi’n/pin photodiode beyond the visible spectrum. Increased sensitivity in the range of 400 nm-850 nm is experimentally demonstrated. Results show that the spectral current under UV front light irradiation (350 nm) increases with the background intensity in the 470nm-800nm range and decreases for low power wavelengths in the visible range. Under back irradiation the spectral current decreases for wavelengths higher than 550nm and strongly increases beneath them. Under front irradiation and low power intensity the gain is high and presents a well defined peak at 750 nm and strongly quenches in the visible range. As the power irradiation increases the peak shifts to the visible range and can be deconvoluted into two peaks one in the red range and another in the green range. In the blue range the gain is much lower showing the filtering properties of the device at different UV background intensities. Under back irradiation the gain is high in the violet/blue ranges and strongly quenches for higher wavelengths whatever the intensity of the background. Results show that, front background enhances the light-to-dark sensitivity of the medium, long and infrared wavelength channels and quench strongly the low wavelength, depending optical amplification on the background intensity. Back UV background enhances only the channel magnitude in short wavelength range and reducing it in the long ones.

Resume : In order to design novel optimized compositions with improved MIEC (Mixed Ionic Electronic Conducting) properties for IT-SOFC cathodes it is of high importance to: 1) acquire a better understanding of the oxygen incorporation, oxygen diffusion and surface reconstruction processes and 2) achieve fast screening of new materials and properties by fine tuning compositions. In this sense, low-energy ion scattering (LEIS) has emerged as a unique technique capable of quantifying the chemistry of the outermost surface with single-atomic-layer sensitivity. In addition, by combining LEIS with oxygen isotope exchange coupled with time-of-flight secondary ion mass spectrometry (ToF-SIMS) it has been possible to correlate exchange kinetics with chemical processes at materials atomic surfaces. Examples of the application of these ion beam analysis techniques for the characterization of epitaxial layered MIEC thin films will be presented, emphasizing the valuable and unique insight provided in the oxygen-incorporation and cation segregation processes. Moreover, by applying the Isotope Exchange Depth Profiling technique to a binary perovskite composition system generated by combinatorial PLD, spatially-resolved oxygen exchange and mass transport properties (k* and D*) have been obtained. This combinatorial approach to material synthesis and characterization has recently opened a new avenue on the generation of entire compositional diagrams in a single experiment.

Resume : Recently, model-type thin film electrodes were demonstrated to be powerful tools for investigation of solid state electrochemical systems. One of their major advantages is that electrochemically active zones are relatively easy accessible by surface analytical methods. Oxygen incorporation zones, for example, can be visualized by polarization-driven 18O tracer incorporation in combination with time-of-flight secondary ion mass spectrometry analysis. In the present contribution, application of this technique to a number of different electrode materials is discussed. By 18O incorporation at Pt electrodes two different reaction pathways could be identified at high cathodic polarization. A successful separation of different oxygen reduction pathways was also possible for La0.8Sr0.2MnO3-δ (LSM) electrodes. Under lower polarization a surface path with oxygen incorporation at the three-phase boundary is found to dominate, whereas at higher cathodic polarization a bulk path becomes more pronounced. Measurements on La0.6Sr0.4CoO3-δ (LSC) and La0.6Sr0.4FeO3-δ (LSF) in 18O2 illustrate the limitations of the tracer incorporation method in case of very high electrochemical activity (LSC) and due to polarization-induced changes of the electrode’s electronic conductivity (LSF). Finally, reaction zones of cathodic water reduction at SrTi0.7Fe0.3O3-δ (STF) electrodes were investigated in a H2/H218O atmosphere and results are compared with electrochemical impedance measurements on this system.

Resume : Solid oxide fuel cells (SOFCs) have been attracting much interest as alternative energy conversion system for next generation. At present, improvement of long term stability is strongly required for SOFC and one reason for decrease in power density could be assigned to the sintering of porous anode, Up to now, three phase boundary is considered as the active site for anode. In this study, we applied La(Sr)Fe(Mn)O3 film as a dense anode for low temperature SOFCs. 　 Dense La(Sr)Fe(Mn)O3-δ (LSFM) nano-film anode is introduced between a Ni–Fe metallic support and LaGaO3 based oxide electrolyte. It was found that the cell using LSFM thin film anode exhibits much improved power density comparing with that of cell with a simple porous Ni-Fe anode. The maximum power density of the cell having LSFM film is approximately 3.0 W/cm2 at 973 K. The improved power density is mainly originated from enhanced anodic properties. Furthermore, the dense LSFM thin film anode is effective for increasing fuel utilization of Ni-Fe metallic anode supported cell. This suggests that two phase boundary (anode and gas phase) is also highly active for anodic reaction. The cell stably shows high power density over reasonably long period. This could be explained by the low dependency of anodic overpotential of LSFM on fuel concentration. Consequently, this study reveals that two phase boundary of LSFM/gas phase is highly effective for high energy conversion efficiency of SOFC.

Resume : Owing to their wide applications in oxygen sensors, multi-layer ceramic capacitors (MLCC), positive temperature coefficient resistors (PTCR), etc., doped SrTiO3 and BaTiO3 are one of the most important electroceramics. Perovskite structure can tolerate high concentrations of defects, for example, oxygen vacancies, electrons and holes, without changing its structure. Defect reactions and reaction parameters of SrTiO3 and BaTiO3, published in literatures, over the doping range from acceptor to donor, temperature range from room temperature to >1500 K and oxygen partial pressure range of 10^-23 to 1 bar are summarized in this work, and a Windowsbased DefectChemCal program is developed. With the program, we can calculate the defect concentrations and the electrical properties of acceptor and donor-doped SrTiO3 and BaTiO3, and the validity of the program is demonstrated by comparing the calculation results and experimental results.

Resume : Rechargeable all-solid-state lithium batteries are attractive power sources for small scale applications and electrochemically stable Li+ fast ion conductors (FIC) can help to widen their application field. Identifying stable fast ion conductors is thus the key to building practical solid-state batteries. Among the most promising compounds with high ionic conductivities are the thiophosphate-based solid electrolytes. Our studies shed light on the role of disorder in the immobile sublattice as a crucial factor for maximizing their conductivity. This is exemplified both for argyrodite-type halide-doped thiophosphates Li6PS5X (where the S2-/X- disorder for X = Cl, Br opens up local paths for Li+ motion), Li7P3S11, Li9+xGexP2-xS12 (LGPS, where local P/Ge disorder limits the packing density) and isostructural compounds in comparison to a series of known and newly designed thiophosphates. Ab initio structure optimisations and bond-valence based atomistic simulations highlight the role of free volume for fast ion transport and the effect of the chemical sulfur-bonding on the structural and electrochemical stability of the compounds. To reduce the synthesis costs of the thiophosphate solid electrolytes, we designed low temperature or no heating routes for their preparation. Electrochemical impedance studies and the performance of these solid electrolytes in all solid state Li-ion and Li-sulfur batteries (reaching theoretical capacity) will be presented.

Resume : Sr-doped lanthanum manganite (LSM) is a widely used cathode material in commercially produced solid oxide fuel cells (SOFC). Despite being a poor ion conductor, LSM electrodes may reduce oxygen via different pathways: a path which includes surface diffusion of oxygen species (surface path) and a path based on oxygen bulk diffusion (bulk path). Separation of effective reaction rates on LSM cathodes into contributions of each path is experimentally highly non-trivial. Accordingly, a detailed knowledge of the rate limiting steps and their dependence on experimental parameters is still missing. In this contribution several methods are employed to identify, quantifying and modify the oxygen reduction paths of (La0.8Sr0.2)MnO3 and (La0.8Sr0.2)0.95MnO3 thin film model electrodes: (i) LSM films on strontium titanium oxide (STO) and yttria-stabilized zirconia (YSZ) with different microstructures, from epitaxially growth to columnar textured, were investigated by 18O tracer diffusion. Numerical analysis allowed separating surface exchange and bulk diffusion properties of both, grains and grain boundaries. (ii) Impedance spectroscopy was used to measure polarization resistances and capacitive effects of micro-patterned and macroscopic thin film, dense LSM microelectrodes. Three phase boundary length and exposed surface areas were varied. (iii) Field driven 18O incorporation and subsequent SIMS analysis revealed quantitative information on the contributions of both reaction paths.

Resume : Novel thin film fuel cell based on the 100 nm-thick electrolyte of amorphous ZrP2.5Ox, working at 400C, was demonstrated. The hydrogen permeable membrane fuel cell (HMFC) using a Pd foil　as a nonporous solid anode was fabricated. Ni interlayer of several hundreds nm thickness was introduced between the Pd anode and the ZrP2.5Ox electrolyte in order to suppress the deterioration of the electrolyte nanofilm by the deformation of the Pd anode during hydrogen absorption. In the ZrP2.5Ox electrolyte the transport number of proton was unity at 400C as determined by an EMF measurement. The modification of the Ni anode surface by an ultrathin Pt or Pd layer effectively decreased the anode/electrolyte interfacial polarization. Consequently, the HMFC revealed the OCV of 1.0 V and the maximum power density of 20 mW cm-2 at 400 degree C.

Resume : Y-doped barium zirconate (BZY) is a proton conductor with good chemical stability and high protonic conductivity. It is a promising candidate as an electrolyte for solid oxide fuel cells in the intermediate temperature range (400-700 °C), and therefore a possible alternative to oxygen ion conductors. It has been shown that BZY with compressive stress results in larger bulk activation energies for proton migration. By extrapolation, it is expected that tensile lattice distortions may lower the activation energy leading to larger proton conductivities at lower temperatures. However, up to date no experimental evidence has been reported on this effect of tensile stress. For this work, pulsed laser deposition is used for the fabrication of higly textured BZY thin films. Epitaxial thin films free of high angle grain boundaries have been grown with the fully relaxed crystalline structure, in compressive and in tensile stress. In our deposition chamber two in situ diagnostics, i.e. Reflective High Energy Electron Diffraction (RHEED) and a Multi-beam Optical Stress Sensor (MOSS) are combined for the first time. This combination allows an understanding of the connection between the growth mechanism and the stress generation/evolution during film growth. X-ray diffraction (XRD) is employed to characterize the crystalline structure, while electrical characterisations will be performed and correlated to the stress state and the growth mechanism, as revealed by MOSS, XRD, and RHEED.

Resume : Electrical Double Layer Capacitors (EDLCs), also known as supercapacitors, are electrochemical energy storage devices for high power delivery or energy harvesting applications [1]. EDLCs store charge through the reversible adsorption of ions from an electrolyte onto high surface area carbons, thus charging the double layer capacitance. Large-size ECs are already used today for power supply and energy harvesting in various applications such as aeronautics, tramways, HEVs (…) [1]. The recent boom in multifunction portable electronic equipment and the increasing need for wireless sensor networks for the development of smart environments has raised the problem of developing sufficiently compact or flexible energy storage. Designing efficient, miniaturized energy-storage devices that can achieve high energy delivery or harvesting at high discharge rates with a lifetime that matches or exceeds that of the machine being powered remains a challenge. Integrating the storage element as close as possible to the electronic circuit (directly on a chip) is another challenge. This talk will present an overview of the results obtained using carbons in micro-supercapacitors. We will show results obtained using exohedral and microporous carbons, as well as bulk carbon films in micro-devices prepared from different methods. The performance achieved to date addresses the need for microscale energy storage in numerous areas where electrolytic capacitors cannot provide sufficient volumetric energy density, such as nomad electronics, wireless sensor networks, biomedical implants, active radiofrequency identification (RFID) tags and embedded microsensors. References [1] P. Simon and Y. Gogotsi, Nature Materials, 7 (2008) 845-854.