Substitution & recycling of critical raw materials in optoelectronic, magnetic & energy devices III

Resume : Since sunlight can be used as a future light source, it is necessary to construct a system that efficiently transfers charges to the reaction site using visible light, which has 47% of the energy required for the photolytic decomposition of water. One of the approaches for this issue is introduced visible responsible range by organic dyes into photocatalyst, called dye-sensitized photocatalyst. Because these anchor sites can be hydrolyzed under the dye-sensitized type photocatalytic reaction conditions, the photocatalytic activity is only maintained for a period of 10?20 h. We have developed the pyridyl anchored type photocatalytic system for stable dye-sensitized type photocatalyst. The pyridyl groups are a potential candidate to serve as an effective anchor group for the metal oxide surfaces in the dye-sensitized solar-energy conversion systems. This type of anchor group can coordinate with the metal oxide by hydrogen bonding coordination. As a result, pyridyl group coordinated molecules showed higher stability activity for photocatalytic hydrogen production in water medium under visible light (over 100 h) . Here, we would like to report new pyridyl anchored type dye-sensitized photocatalytic hydrogen production. Boron-dipyrromethene (BODIPY) are compounds with specific absorption at 600-700 nm. We have successively introduced on the surface of TiO2 photocatalyst for dye-sensitized photocatalyst. As a result, these dyes modified photocatalysts showed stable visible light driven photocatalytic hydrogen production activity over 100 h and showed as high as 0.8% apparent quantum efficiency at 650 nm with BODIPY dye-modified TiO2 photocatalyst.

Resume : Hydrogen production through solar-water splitting can be a viable solution towards a more environment-friendly energy economy. Such technology suffers from the cost of the catalysts, being Pt and RuO2 or IrO2 the reference materials used for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Here, we report on a low-cost approach to synthesize Ni(OH)2 nanowalls (NW) acting as efficient catalyst for OER. Working electrodes were fabricated by growing thin films (< 0.2 µm) of Ni(OH)2 NW by combining chemical bath deposition and post-growth surface oxidation. We systematically studied the morphology and chemical arrangement before and after OER through SEM-EDX analysis, while the catalyst loading, its chemical composition and the presence of dopant impurities have been investigated by Rutherford backscattering spectrometry (RBS) and XPS. Electrochemical measurements were performed to study the OER catalytic activity under alkaline conditions (1M KOH). We optimized the synthesis up to get a significant improvement in the OER performance, with a long-term stable overpotential down to 320 mV at 10 mA/cm2 and a O2 turnover conversion frequency up to 0.1 s-1, by employing NiO NW. Such values can be further improved when an additional dopant (like Fe or Co) is added. Our findings confirm how such facile synthesis of NiO/Ni(OH)2 NW can be employed as a viable low-cost method to create efficient platform catalysts, without the use of critical raw materials.

Resume : Effective water splitting via electrolysis driven by renewable energy requires highly active catalysts to minimise the sensitivity of the hydrogen (H2) generation rate to fluctuating operating conditions . NiMo can potentially replace platinum as hydrogen evolution reaction (HER) catalysts because of their low overpotential over the entire pH range. However, it is still not understood if the low HER overpotential is due to high intrinsic catalytic activity or extrinsic factors, such as increased surface area or mass loading. We used electrochemical impedance spectroscopy to study HER kinetics of NiMo electrodeposited on fluorine-doped tin oxide glass in alkaline, neutral and acidic media. The higher HER activity in acidic media was found to be accompanied by more favorable H2 adsorption and charge transfer kinetics compared to those in neutral and alkaline media. While two Tafel regions were observed for acidic and neutral media, only one was observed for alkaline media . Preliminary data from fitted impedance spectra indicated that in low overpotential regions (|?|< ~0.15 V for acidic and |?|< ~0.10 V for neutral ), the HER catalysis is mainly governed by H2 adsorption kinetics, while in high overpotential regions it is controlled by charge transfer kinetics. Experiments on the effects of surface roughness, catalyst thickness and electrolyte stirring on HER kinetics are ongoing to confirm intrinsic catalytic properties in different pH regions.

Resume : Platinum group metal-free electrocatalysts have shown promising features for catalyzing oxygen reduction reaction (ORR) at the cathode of different types of fuel cells [1-3]. However, high costs for synthesis, stability and activity issues under operating conditions, still limit their applicability. We propose a facile synthesis strategy to obtain Fe-N-C ORR catalysts consisting on a nitrogen and iron wet impregnation of carbon black followed by pyrolysis steps. Three different nitrogen sources (dopamine, imidazole and benzimidazole), and two different pyrolysis atmospheres (Ar and NH3) were used. The obtained materials were characterized in terms of structure, morphology, surface chemistry, thermal and electrochemical properties. Tailoring the synthesis parameters allowed obtaining electrodes with a high porosity and density of active sites to boost catalytic towards ORR in alkaline environment, as indicated by X-ray photoelectron spectroscopy, cyclic and linear sweep voltammetry with rotating disk electrode. In particular we found that the pyrolysis step under ammonia flow led to high double layer capacitance electrodes with high porosity and the use of imidazole as nitrogen-rich organic precursor improved ORR activity as compared to control Pt-based electrodes. References 1. Thompson et al. Nat Catal, 2019, 2, 558. 2. Mecheri et al, Appl Catal B-Environ, 2018, 237, 699. 3. Artyushkova et al. ACS Appl. Energy Mater. 2019, 2, 5406.

Resume : The low temperature phase (LTP) of MnBi, with hexagonal crystal structure, is receiving increasing attention due to its high magnetic anisotropy (1.6 MJ/m3) and Curie temperature (711 K), as well as to the outstanding increase in coercivity with temperature, which makes it ideal for high temperature permanent magnet applications, including microscale sensors and energy harvesters. LTP-MnBi microcrystals of different size have been prepared as hexagonal islands on glass substrates by RF-magnetron sputtering of composite targets. Atomic force microscopy shows crater-like shapes, with the outer parts about one order of magnitude thicker than the central zone ( 0.2 m). The microcrystals exhibit perpendicular magnetic anisotropy with coercive fields (up to HC = 10.7 kOe) dependent on the substrate temperature during deposition (TD). At higher TD (475 K), the morphology of the LTP-MnBi microdeposits changes to rods lying on the substrate plane, which display in-plane anisotropy with a remarkable coercivity of HC = 20 kOe at T = 400 K. Finally, ongoing efforts on the utilization of the above LTP-MnBi as a matrix to embed high saturation magnetization FeCo nanoparticles (in order to enhance the energy product through exchange-coupling) will be presented. These soft particles are pre-formed by gas-phase condensation in an ancillary chamber and then injected as a beam into the main chamber, where they are co-deposited with the MnBi matrix.

Resume : Simultaneous co-existence of room-temperature ferromagnetism and ferroelectricity in Fe doped BaTiO3 (BTO) is intriguing, as such Fe doping into tetragonal BTO, a room-temperature ferroelectric, results in the stabilization of its hexagonal polymorph which is ferroelectric only below ~80K. Here, we investigate its origin and show that Fe doped BTO has a mixed-phase room-temperature multiferroicity, where the ferromagnetism comes from the majority hexagonal phase and a minority tetragonal phase gives rise to the observed weak ferroelectricity. In order to achieve majority tetragonal phase (responsible for room-temperature ferroelectricity) in Fe doped BTO, we investigate the role of different parameters which primarily control the paraelectric hexagonal phase stability over the ferroelectric tetragonal one and identify three major factors namely, the effect of ionic size, Jahn-Teller (J-T) distortions and oxygen-vacancies, to be primarily responsible. The effect of ionic size which can be qualitatively represented using the Goldschmidt's tolerance factor seems to be the major dictating factor for the hexagonal phase stability. The understanding of these factors not only enables us to control them but also, achieve suitable co-doped BTO compounds with enhanced room-temperature multiferroic properties.

Resume : La< sub>1-x< /sub>Dy< sub>x< /sub>Mn< sub>1-y< /sub>Zn< sub>y< /sub>O< sub>3< /sub> system belongs to the family of perovskites-ABO< sub>3< /sub>- and it contains two well-defined magnetic sublattices. In this work, we study the influence of magnetic dilution on the magnetic properties of the system for x = 0.0, 0.05, 0.1 and y = 0.0, 0.05, 0.1 at temperatures between 10 K and 300 K. For the diluted samples, the field-cooled magnetization (MFC) at 10 Oe shows a change of paramagnetic to ferromagnetic order. Below Tc, the large difference between MFC and zero field-cooled magnetization (MZFC) as well as their bifurcation are factors that suggest a glassy behavior. In our case, the measurements suggest an antiferromagnetic inhomogeneous long-range order followed by a canted antiferromagnetic order at lower temperatures. The magnetization results have been correlated by electron magnetic resonance measurements in the temperature range 5 K < T < 300 K

Resume : Co3O4 is a material of interest for thermochemical solar energy storage, however, it is desirable to alloy this compound with Mn3O4 to reduce the stoichiometric ratio of Co due to the expense of this component. In this work, we use machine learning techniques with moment tensor potentials (MTPs) [1] and artificial neural networks (ANNs) [2] to predict the phase stability of CoxMn3-xO4 alloys. The utilisation of machine learning techniques in materials science is enabling the typical time- and length-scale boundaries of density functional theory (DFT) based methods to be pushed further. The total possible configuration space of an alloy is an example of a system that can be too computationally demanding to study exhaustively with DFT methods. However, the energies of all possible configurations are necessary to investigate entropic stabilisation of alloys. Using MTPs and ANNs we are able to predict the energy density of states for the full alloy configuration space of millions of structures, starting from a training set of only hundreds of structures. [1] A. V. Shapeev, Moment tensor potentials: A class of systematically improvable interatomic potentials, Multiscale Modeling & Simulation14, 1153 (2016). [2] A. S. Bochkarev, A. van Roekeghem, S. Mossa and N. Mingo, Anharmonic thermodynamics of vacancies using a neural network potential, Physical Review Materials 3, 10.1103/physrevmaterials.3.093803 (2019).

Resume : Recently a computational proxy was developed to identify new magnetocaloric materials whereby first principle structure relaxation is carried out with and without spin polarization to ascertain the degree of magnetic deformation (Chem. Mater., 29, 1613-1622, 2017). By applying this method to ferromagnet in the PbFCl family we found magnetic deformation of around 2% which is similar to other magnetocaloric compounds. We therefore have focused our experimental study on MnZnSb, which is reported to be an itinerant ferromagnet with a second order phase transition and Curie temperature about room temperature (Jap. J. Appl. Phys., 32, 273, 1993). Detailed magnetization measurements were carried out and Arrott analysis yields a Curie temperature of 304K, with the system being described as a 3D itinerant ferromagnet from the critical exponents of the Arrott-Noakes equation. We find a reasonably large magnetic entropy change of 4.5 Jkg-1K-1 with a relative cooling power of 153 Jkg-1; which is comparable to second order compounds with about room temperature transition temperatures. Heat capacity measurement shows an anomaly around the magnetic transition and together with the magnetometry can be used to calculate an adiabatic temperature change of 2 K under 2 T. Temperature dependant powder neutron diffraction was used to investigate the origin of the significant magnetic entropy change around the magnetic transition.

Resume : Black aluminium is a metal with a cauliflower surface morphology favouring a moth-eyes effect. A high light absorbance results from these structures explaining the black appearance of these films. Aluminium has the advantage to be cheap and the most abundant metallic element. Black aluminium films were deposited on different subtracts as fused silica, glass, and metallic surfaces, using DC pulsed magnetron sputtering in a mixed atmosphere of argon and nitrogen. Conditions in the N2/Ar mixture in the film growth were studied and black film growth was observed with a nitrogen percentage of 6%. An ultra-high absorbance of 96.6% was measured for a wavelength range from 300 nm to 1100 nm. Black aluminium films presented a metallic behaviour slightly degraded in comparison to aluminium film. Then, these layers were deposited on Quartz Crystal Microbalance (QCM) sensors in order to increase the active surface areas of electrodes. A change of the resonance frequency was reported and a clear improvement in the QCM response was measured. Black aluminum was also deposited on pyroelectric films to convert light energy into heat, and then the heat energy into a pyroelectric current. Large temperature variations induced by the high light absorbance double the polarization variation reported across the pyroelectric samples.

Resume : The strong dependence of humans on fossil fuels during the last centuries has generated an alarming global environmental damage. In order to change this situation and minimise the caused damage, is proposed the technological transition from synthetic materials toward a new generation of natural based ones. In this aim, we have selected Silk, a natural macromolecular protein produced by Bombyx Mori silkworms as one of the most promising materials. Silk fibers are among the strongest materials obtained from nature and thanks to the extended silkworm breeding are easily accessible. Silk has been naturally endowed with excellent thermal and chemical stability, high mechanical strength and biodegradability. Further, silk is highly processable and some works have reported its piezoelectric response. In order to explore Silk potentiality and contribute to natural based materials transition, this works reports a series of fully functional Silk based devices. For that, Silk original shape was initially modified as fibres, films, mats, membranes, gels and particles. Secondly, obtained new morphologies were combined with complementary fillers in order to improve their intrinsic properties. Thereby, transparent and conductive layers, piezorresistive sensors, magnetic and electric bending responsive actuators and polymeric Li-batteries were obtained. Actually, a full line of functional and active devices have been processed from Silk. Thanks to this advances, is has been demonstrated that really exist a choice for synthetic materials to natural ones transition, approaching us to a future linked with nature and less harmful with our environment.

Resume : Recycling chlorine resource has caused widespread concern, and the catalytic oxidation process is one effective method. However, hydrogen chloride oxidation is a strong exothermic reaction, and the reaction temperature is difficult to control in the fixed bed reactor. the fluidized bed with the advantage of fast heat moving is adopted in this process. Y molecular sieve-kaolin as support and aluminum sol-silica sol as binder were used to the preparation of CeCuK/Y fluidized bed catalyst, and a suitable two-step preparation process was selected to reduce the sticking to the wall in the spray process. BET, SEM, XRD, Wear index tester were used to characterize the catalyst. Catalyst activity was investigated in a fluidized bed, and under the condition of reaction temperature 430 ℃,volume ratio of hydrogen chloride to oxygen 1:1, space velocity 1.0 h-1, the maximum conversion of hydrogen chloride reached 82%.

Resume : In order to obtain a high-performance absorber, the Ce15.6Co81.2-xFe3.2Cux (x=0.0, 1.6, 4.8, 8.0, 11.2) powders were prepared via the method of arc melting and high energy ball milling. The structure, morphology, composition and electromagnetic parameters of the samples were examined by variously analytical techniques. The results of phase structure indicated that the all powders mainly consisted of single phase CeCo5. The morphology of the powders were sheet with high aspect ratio, which was conducive to achieve the excellent absorption performance. The absorption peak frequency of Ce-Co-Fe-Cu powders moved to low frequency in the range of 1.6-2.0 mm and all minimum reflection loss (RL) values were less than -20 dB. For the sample excluding Cu, the minimum RL was -37.35 dB at 11.12 GHz with the thickness of 1.8 mm. At the thickness of 1.9 mm, the minimum reflection loss (RL) value of Ce15.6Co79.6Fe3.2Cu1.6 could reach -34.79 dB at 9.6 GHz. All results suggested that the powders are promising electromagnetic wave absorption materials with a good performance.

Resume : Since many years, some raw materials used in photovoltaic technology (such as indium, germanium…) were classified as critical which may constitute a serious problem for the perennity of thin film solar cells. In order to ensure the perennity and development of thin film solar cells, we must substitute the classical materials (CIGS, CdTe…) with critical raw materials-free such as Cu2ZnSnS4. Cu2ZnSnS4 and sodium doped Cu2ZnSnS4 (Cu2ZnSnS4:Na) thin films were successfully deposited by vacuum thermal evaporation method. Na concentration varied from 0 to 7 at. %. The effect of Na doping on the optical and electrical properties of the Cu2ZnSnS4 thin films was investigated. The optical, structural and electrical properties were studied using UV-Vis-NIR spectroscopy, X-ray diffraction (XRD) and AC impedance spectroscopy, respectively. The optical properties of Cu2ZnSnS4:Na thin films were calculated the transmittance and reflectance data. With the increase of the Na concentration, the band gap of the films increased gradually from 1.52 to 1.90 eV for sodium doping of 0-7 %. The XRD analysis confirms the existence of Cu2ZnSnS4 phase with the preferential plane (112). Electrical properties have been investigated by AC impedance spectroscopy over a wide range of temperature up to 285 °C starting from room temperature in the frequency range 5 Hz–13 MHz. The complex impedance plots display one semicircle with equivalent circuit functions as typical parallel RC. Cu2ZnSnS4 material could substitute CIGS as a cost-effective and earth abundant absorber in thin film solar cells.

Resume : Transparent conducting ceramic films are of high technological interest to replace traditional transparent conducting oxides such as indium-tin oxide (ITO) and F-doped SnO2 (FTO) that are widely used in electrochemistry and in related applications like in dye-sensitized solar cell (DSC). In particular, there is a strong demand for the replacement of ITO and FTO for DSC application owing the thermal instability of ITO and the formation of a Schottky barrier at the heterojunction photoanode interface of TiO2 with both ITO and FTO. Here, we briefly report on the preliminary experimental results of a work-in progress study on the synthesis and characterisation of gold nanoparticles (Au-NPs)-doped titania films obtained by using a sol-gel procedure. Transparent Au-NP-doped and undoped sol gel titania coatings were grown on soda lime glass and (100)-Si-substrates and heat treated in air at 500°C after deposition. The chemical composition, morphology and microstructure of the films was investigated in detail by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and X-ray scattering (XRD and XSR). A four-point probe method was used to measure the sheet resistance of the layers to avoid contact resistance. The results show that the films are free from organic residues and are constituted of nanocrystalline titania (crystallite size about 12nm ) in anatase structure with embedded Au NPs (crystallite size: between 10nm and 20nm). The presence of the Au NPs in the titania matrix gives rise to a sharp lowering of the sheet resistance up to < 20 ohm/sq. This finding suggests that Au-NPs titania nanocomposites could be considered as transparent conductive layers to replace ITO and FTO in order to fabricate electrocatalyst supports for electrochemical applications. However, further studies are necessary and are currently under way in our laboratories.

Resume : Structural, optical and electrical properties of (Ytterbium/Terbium) co-doped ZnO thin films deposited on glass substrates by spray pyrolysis method were investigated. The films exhibited the hexagonal wurtzite structure with a preferential orientation along [002] direction. No secondary phase was observed in the X-ray diffraction detection limit. Atomic force microscopy (AFM) was performed and a root mean squared roughness (RMS) of our samples decreased with Terbium content. Photoluminescence measurements showed a luminescence band at 980 nm that is characteristic of Yb3 transition between the electronic levels 2F5/2 to 2F7/2. This is an experimental evidence for an efficient energy transfer from ZnO matrix to Yb. Hall Effect measurements gave a low electrical resistivity value around 6.0 10-3 Ω.cm. Such characteristics make these films of interest to photovoltaic devices.

Resume : Conventional vapor-compression refrigeration technology has practical limitations because of its environmental destruction. Recently, new cooling technologies to replace it have been underway, including thermoelectric cooling, thermoacoustic refrigeration, and magnetic refrigeration, etc. Among them, magnetic refrigeration is based on the thermodynamic magnetocaloric effect (MCE). In this presentation, microwave hydrothermal synthesis was employed to fabricate DyVO4 nanowires as a MCE material for hydrogen liquefaction. During synthesis, EDTA was added as a chelating agent to obtain uniform DyVO4 nanowires (sample A), and their magnetic properties were compared with those of irregular shaped DyVO4.nanoparticles (sample B). The structure and morphology were studied by using scanning electron microscope (SEM) and transmission electron microscope (TEM) measurements. The Neel temperature (TN) of the sample A was higher than that of the sample B due to suppression of antiferromagnetism induced by the size effects of the sample B. The Curie-Weiss fitting showed the weak antiferromagnetism for the both samples. However, the effective magnetic moments for the both samples had lower values than that of bulk DyVO4 because of the size effects, where uncompensated spins on the surface of the nanostructures induce suppression of antiferromagnetism. The maximum magnetic entropy change (-ΔSM) of the sample A was higher than that of the sample B at H = 50 kOe, and consequently led to an increase in relative cooling power (RCP), a measure of MCE. It is known that DyVO4 has a structural transition from tetragonal to orthorhombic symmetry around 14 K due to the Jahn-Teller effect induced by the ordering of quadrupole of Dy3+ ions [1]. The magnetic entropy changes (- ΔS) with temperature showed an anomaly of -ΔS due to the Jahn-Teller effect for the both samples, which was dependent on the strength of the magnetic field. The quadrupole coupling of DyVO4 resulted in an enhancement of RCP due to an increase of the full width of the maximum of temperature. [1] A. Midya, N. Khan, D. Bhoi, P. Mandal, Physica B, (2014) 448, 43-45.

Resume : Study on Cobalt-Ionic Liquids interaction to design new thermochromic materials. Floriana Billeci1, Francesca D’Anna*1, Maria Luisa Grilli*2, Marta Feroci3. (1) Dipartimento STEBICEF – Sezione di Chimica, Università degli Studi di Palermo, Viale delle Scienze, Ed. 17, 90128, Palermo, Italy (2) Energy Technology Department, ENEA, Casaccia Research Centre, Rome, Italy (3) Department SBAI, Sapienza University of Rome, via Castro Laurenziano, 7, 00161 Rome, Italy The numerous research studies on Ionic Liquids (ILs) and the disparate fields of applications are based on their well-known advantageous properties. Hence, in this work, a mixture of [bEt3N][NTf2] (solvent) and an IL bearing gluconamide moiety (ligand) were employed in a thermochromic study with Co(NTf2)2.1 Gluconate fragment (therefore multiple hydroxyl groups) in the cation and the bromide anion display interaction with the cobalt salt. This interaction shows a thermochromic octahedral (pink) – tetrahedral (blue) configuration change depending on the temperature. Meantime, from the trend of the absorbance, the temperature of the transition can be determined. The working temperature range (10-100 °C) and, even more, the transition temperature (60 °C) opens the way for the potential application in the thermosensitive devices field.2 In order to make this goal possible, the ratio ligand/metal, the IL used as the solvent and the structure of the IL ligand were taken into account. 1. S. J. Osborne, S. Wellens, C. Ward, S. Felton, R. M. Bowman, K. Binnemans, M. Swadzba-Kwasny, H. Q. N. Gunaratne, P. Nockemann, Thermochromism and switchable paramagnetism of cobalt(II) in thiocyanate ionic liquids. Dalton Trans. 44 (2015) 11286-11289. 2. K. Zhang, M. Zhang, X. Feng, M. A. Hempenius, G. J. Vancso, Switching light transmittance by responsive organometallic poly(ionic liquid)s: control by cross talk of thermal and redox stimuli, Advan Funct Mater 27 (2017), 1702784-n/a. Presentation preferred – Select the appropriate method Poster presentation preferred

Resume : Energy conversion using thermoelectric material have been one of the most challenging method. Epically. Bi2Te3 has been a representative thermoelectric semiconductor with a relatively high electrical conductivity and lower thermal conductivity. The efficiency of thermoelectric materials is generally expressed as figure of merit, ZT = S²σT/κ, where σ is the electrical conductivity, S is the Seebeck coefficient, and κ is thermal conductivity. In order to improve the ZT, various methods such as doping, nano-structuring, or introducing nanomaterials has been researched, which are relatively expensive and complex methods. In this study, we attempted to get lower thermal conductivity by reducing the grain size by using simple and inexpensive milling process. For enhancing the uniformity of the particle size distribution, additional sieving process of Bi2Te3 powder were employed. The milling process decrease particle size of Bi2Te3, leading to reduction of grain size of sintered samples. The reduced grain size causes the more phonon scattering at the grain boundary, resulting in enhancing the ZT in all of milled samples of Bi2Te3. The highest ZT value were measured to be 0.84 at 423 K in the additionally-sieved samples. This result proposes the size and uniformity of the Bi2Te3 powder should be considered as important factors to improve the thermoelectric properties.

Resume : Materials having colossal dielectric constant (CDC) and low loss (ε_r≥10^3 and dielectric loss tanδ≤0.1) with good frequency stability is crucial for device miniaturization and high-energy density storage application. Hu et al [1] recently reported a temperature and frequency independent CDC with a low dielectric loss in acceptor-donor co-doped TiO2. The CDC is postulated to be originated from electron-pinned defect dipoles which is the acceptor-donor defect complex, though the detail mechanism and experimental evidence are lacking. Li-Al co-doped ZnO, Zn0.99(Li0.1, Al0.2)0.033, ceramic exhibits a colossal dielectric constant (CDC) with good frequency stability, which have a dielectric constant of ~10000 at the frequency of 1 kHz. Impedance spectroscopy shows that the CDC phenomenon is not associated with the internal barrier capacitance (IBLC) effect. M''(f) spectrum obtained from electric modulus (M^*=M^'-jM'') analysis reveals two relaxation processes P1 and P2. Frequency dependent ac conductivity data can be well fitted by the Correlated Barrier Hopping (CBH) model, showing that the CDC would be originated from the thermally activated electron hopping between two neighboring acceptor-donor defect complex sites over their Columbic barrier. A simple model involving these acceptor-donor defect complex dipoles and the Cole-Davidson distribution of relaxation time [2,3] can explain the CDC phenomenon with good frequency stability.

Resume : For application to tri-packaged white down-converted light-emitting diodes (DC-LEDs), we used the hot injection method to synthesize bright and eco-friendly green Ag-In-S/Zn-In-S/ZnS (AIS/ZIS/ZnS) quantum dots (QDs). To obtain bright green AIS/ZIS/ZnS QDs, we proposed a ZIS inner-shell to reduce lattice mismatch between AIS core and ZnS outer shell. Two variables of shell precursors, low concentration and high concentration of zinc acetate dihydrate, were chosen to form the ZIS inner-shell. Unlike a low concentration of zinc acetate dihydrate, a high concentration of zinc acetate dihydrate using an exothermic reaction can lead to the formation of ZIS inner-shell and bright green AIS/ZIS/ZnS QDs. We also confirmed the formation of the ZIS inner-shell by Raman spectroscopy and X-ray diffractometry. The synthesized green AIS/ZIS/ZnS QDs showed a high photoluminescence quantum yield (PLQY) of 0.84 with a peak wavelength of 505 nm. For application to tri-packaged white DC-LEDs, we used red Cu-In-S/ZnS (CIS/ZnS) QDs synthesized using hot-injection method, the obtained green AIS/ZIS/ZnS QDs, and a blue InGaN LED. In addition, tri-packaged white DC-LEDs are realized at a correlated color temperature (CCT) in the range of 2700 K to 10000 K. The realized tri-packaged white DC-LEDs showed a high luminous efficacy (LE) value of 85 lm/W at applied current of 180 mA, color rendering index (CRI, Ra) of 93, and external quantum efficiency (EQE) of 0.30 at 5700 K.

Resume : The demand for the platinum group metals has increased over recent years due to the fact that around 60 percent of the world's annual output of platinum group (PGM) metals, particularly platinum (Pt), palladium (Pd) and rhodium (Rh), is utilized to manufacture automotive catalysts, known as catalytic converters as well. The automotive catalysts neutralise the toxic gases with the percentage above 90%. They catalyse the reduction of NOX, oxidation of HCs and CO to N2, CO2 and H2O. However, natural sources of PGMs are relative poor and thus it is important to develop efficient methods both economically and environmentally for recovering PGMs from secondary sources, suchlike catalysts used in the vehicles. PGM recovery methods are categorized into pyrometallurgical, hydrometallurgical, or biometallurgical, without regard to the source of PGM. The use of the correct metallurgical method largely depends on the sort of metal and the energy cost needed to process the waste. Here, a simplex and eco-friendly method was suggested in order to recover Pd from the spent catalyst on the basis of Al2O3 carrier. Respective catalyst used to be mounted and utilized orginally in a passenger car and it was coated by a thin film of Pd in the form of porous Al2O3 structure. To ensure the optimum recovery of Pd, a solution of distilled hydrochloric acid (HCl) and hydrogen peroxide (H2O2) were studied. Finally, addition of formic acid (HCOOH) was applied for separating Pd from the solution. The efficiency of the leaching was reported as 95% in response to the heat treatment at 80°C for 1.5 hours along with solid/liquid ratio of 1/9.5. Additional thermal process at 100°C for 1 hour was adequate to obtain efficiency of 95% for Pd recovery.

Resume : The renewed interest in permanent magnets based in the ThMn< sub>12< /sub>-type compounds is driven by their reduced content of critical elements and the current availability of advanced processing techniques scalable to the industry. As the nitride Nd(Fe,Mo)< sub>12< /sub>N< sub>x< /sub> compound show promising intrinsic properties, as high anisotropy field (>10T) and high saturation polarization (>1T), several processing routes to obtain high extrinsic ones were studied in this work. We investigate the fabrication and nitrogenation process of melt-spun NdFe< sub>10.5< /sub>Mo< sub>1.5< /sub> in order to obtain high coercivity powders for bonded and printed magnets. Nitride powders with Curie point of 370 ºC, a coercive field of 0.55 T and saturation polarization of 1 T were used as filler material in the manufacture of resins for bonded magnets and inks and filaments for screen- and 3D-printed magnets. Many efforts were made in the manufacture of anisotropic magnets.

Resume : Current advances on permanent magnets are strongly linked with the use of critical raw materials, as rare-earth elements (RE), whose main supplier does not apply eco-friendly policies to the mineral extraction process, avoiding the possibility to develop green technologies recommended by the EU and US governments. The scarcity of these raw materials, required for the development of commercial high-energy permanent magnets, boosts the search of new hard magnetic alloys with a reduced content of critical elements and similar performance to the current commercial magnets. The hard magnetic ThMn₁₂-type phases are promising candidates due to its intrinsic properties; high saturation magnetization (>120 A·m²kg^-1), Curie point (>300 ºC) and anisotropy field (>4 T), these properties were enhanced by the addition of light elements (H, N) at the interstitial sites of the 1:12 crystal structure or by Sm-substitution at the Th site. In addition, progress in the development of coercivity on samples with high anisotropy has been done using different processing methods. The intrinsic properties of the hard magnetic phases were significantly improved by the proposed methods. The maximum coercivity reached in these compounds is above 0.6 T and 1 T in nitride Nd-based and Sm-based 1:12 alloys, respectively. The successful experimental approaches used in this work demonstrate some ways to obtain high-performance permanent magnets with partial substitution of light REs and total substitution of heavy RE elements.

Resume : The present work is focusing to aluminium oxynitride (AlON) that has a unique thermal and chemical stability which makes it the perfect candidate for a wide range of applications. Although there has been extensive research on this material, especially more recently because of increased commercial interest, extensive systematic powder synthesis and processing studies have been carried out to determine alternate, more cost efficient routes to fully dense transparent bodies. Samples alumina-ALN powder mixtures with nano-additions have been prepared and extensive EDS/SEM, XRD and TEM inestigations have been done. The four type of nano-additions with three different quantities were as follows: SiO2 0.35%, 0.45%, 0.55%, MgNO3 0.5%, 1%, 1.5%, CeO2 0.05%, 0.1%, 0.15%, CaCO3 0.3%, 0.4%, 0.5%. The results before attrition milling showed that in starting powder mixtures the distribution of AlN particles in the Al2O3 matrix is not homogeneous. The grain size of the Al2O3 was approximately 100-200 nm and 0.5-1 μm for the AlN. SiO2 was found only in the powder mixture with the highest (0.55%) SiO2 content. Mg was detected with N (where AlN particles could be seen). CeO2 was found only in the powder mixture with the highest (0.15%) CeO2 content. Ca was detected in the all powder mixtures and it occured with N. One hour-long attrition milling resulted in powder mixtures with homogeneous distribution. However, particles with fluor and zirconium content could be seen originating from the tephlon and ZrO2 milling spacers and agitators.

Resume : The influence of the various content of the multilayered graphene (MLG) on the structural and mechanical properties of the final bulk porous silicon nitride-zirconia (Si3N4-ZrO2) based ceramics was investigated. The ceramic composites were prepared in the form of the laminated structure with different (5-30-5 wt% and 30-5-30 wt%) MLG content by hot isostatic pressing. ZrO2 particles were incorporated into the Si3N4 matrix by attrition milling to improve the mechanical properties of the final composite. Homogeneous distribution of the MLGs, a completed phase transition from α to β-Si3N4 in case of 5 wt% MLG have been observed. The structural examinations revealed that the multilayered graphene and zirconia particles owing to their different sizes and shapes influenced the porous microstructure evolution and the related mechanical properties of the composites. The sandwich structures enhanced the mechanical properties compared to reference ceramic with 30 wt% MLG. The position of the layer with higher graphene content, high ratio of alfa/ beta phase of Si3N4 and higher porosity had crucial effect on the final mechanical properties.

Resume : Indium selenide (InSe) is a typical representative of group III-VI layered materials, with a direct band gap of about 1.3 eV and indirect one of 1.26 eV at room temperature. By splitting bulk InSe single crystals perpendicularly to the C6 axis, plan-parallel lamellae with atomically flat surfaces and thickness down to nanometer range can be obtained. InSe lamellae are comprised of elementary Se-In-In-Se packings bound by van der Waals forces, with closed valence bonds at surface. Due to mentioned characteristics, together with nature of optical transitions in the center of Brillouin zone and low surface-state density, InSe is considered among the first 5 most promising materials for photovoltaic, water splitting and transistor technology applications. In this work, through absorption, photogeneration, photoluminescence, EDX and Raman studies, influence of thermal preparation regime of ITO/InSe heterojunctions, as well as of Cd and Sn dopant concentration on the energy band diagram in the oxide/semiconductor interface layer is investigated. At the same time, relationships between the features of photosensitivity spectrum and the characteristics of localized states in the semiconductor layer of the oxide-semiconductor interface are established.

Resume : Tungstate-lanthanum-borate glasses containing different amount of Nb2O5 were obtained by melt quenching technique. The glass compositions (50-x)WO3-25B2O3-25La2O3-xNb2O5, x= 5, 10 and 20 (mol%) were doped with 3 mol% Eu2O3 at the expense of La2O3 in order to examine their luminescence properties. The thermal parameters of the synthesized glasses were evaluated by differential thermal analysis. It was determined that the glass transition temperature increases with the increase of Nb2O5 but the crystallization temperature decreases. The short-range order of the synthesized glasses was determined by IR, Raman and UV-VIS spectroscopies. It was found that the amorphous network is built up with participation of WO6 and WO4, NbO6, BO3 and BO4 units. Photoluminescence emissions due to the 4f transitions 5D0→7Fj (j=0-4) of Eu3+ ions were observed. Influence of Nb2O5 content on the emission intensity of the prepared glasses was established. It was found that the glass containing 15 (mol%) Nb2O5 possesses the most intensive luminescence of Eu3+ ions. The charge transfer at room temperature from tungsten to europium ions was proved while such a transfer from niobium to europium was not observed. Acknowledgments: This work is supported by Bulgarian National Science Fund under project КП-06-Н29/7

Resume : The most widely used transparent conductor electrode (TCE) in organic devices is Indium Tin Oxide (ITO) due to its high optical transparency, metallic conductivity and high work function favoring an efficient injection of holes into many organic semiconductors. Because indium is a critical raw material, expensive, short supply, toxic and difficult to use on flexible substrates, it is necessary to identify new alternative for TCE from cheaper materials showing high transmission and low resistivity for small thickness of the electrodes. This paper presents some investigations on the optical and electrical properties of the heterostructures realized with arylenevinylene oligomer: perylene diimide mixed active layer and 3 layers, oxide/metal/oxide TCE (e.g. ZnO/Ag/ZnO; ZnO/Au/ZnO, AZO/Ag/AZO, AZO/Au/AZO). The 3 layers electrode was deposited by sputtering on glass and optically and electrically characterized in correlation with the morphological and structural particularities evidenced by SEM, AFM and XRD measurements. The heterostructures were characterized by spectroscopic (UV-VIS, Photoluminescence) and microscopic (SEM, AFM) methods and the properties of heterostructures with different types of 3 layers TCE will be compared with those of the same heterostructures realized with ITO electrode. The effect of a supplementary layer of PEDOT-PSS intercalated between the TCE and organic layer on the properties of the heterostructures has been also investigated.

Resume : Environmental problems such as air pollution, soil contamination, especially refractory wastewater produced by some noxious organics, have aroused much attention in the area of environmental remediation. Recently, with a growing demand for clean and comfortable environment, purification technologies with high efficiency and low cost to reduce the pollutant contents of wastewater are urgently needed. TiO2 and ZnO are considered to be one of the suitable materials for photocatalyst due to its nontoxicity, biological inertness, chemical stability and low cost. Despite their obvious advantages, TiO2 and ZnO are a white powder difficult to handle and separate from a liqui solution, hence this problem is eliminated or minimized by various smart solutions. In this study, a facile and efficient approach for the fabrication of Ag coated Fe3O4@ZnO nanoparticles with a good core-shell structure is demonstrated. The magnetic cores of Fe3O4 act as the center for the growth of ZnO nanorods. As a result, the zinc oxide nanorods grown around Fe3O4 magnetic cores form a rod-like hybrid structure. The Fe3O4@ZnO-Ag core-shell microsphere possesses a relatively large specific surface area induced by noble metal nanoparticles, a magnetic behavior for easy reuse, and enhanced photocatalytic efficiency caused by metal-semiconductor chare transfer or energy transfer. As characterized by FE-SEM, HR-TEM and XRD, the as-synthesized Ag coated Fe3O4@ZnO nanoparticles exhibit a narrow size distribution. The Ag coated Fe3O4@ZnO photocatalyst exhibited high photocatalytic activity in the degradation of rhodamine B and methylene blue under solar light and visible light. The photodynamic process of Ag coated Fe3O4@ZnO rapidly generates reactive oxygen species (ROS). Therefore, the detection methods and generation mechanisms of the intrinsic reactive oxygen species (ROS) such as hydrogen peroxide (H2O2), singlet oxygen (1O2) and hydroxyl radical (′OH) in photocatalysis were comprehensively examined. Reactive oxygen species (ROS) confirmed once more under the presence of scavengers. The renewable photocatalytic activity of the photocatalyst was also examined.

Resume : This study reports the influence of the deposition conditions of SiO2 and ZnO oxide thin films on their structural properties. These films were deposited by rf-MS technique on quartz substrates. The film thickness values of 0.100-0.250 μm were measured using an interferometric method. The orientation of crystallites, surface morphology, mass density, structure and composition were investigated by XRD, XRR, XPS and SEM. The maxima and minima of transmission and reflection spectra recorded in the range 200-2500 nm for the analyzed samples are due to multiple reflections on the surfaces of the film, indicating that the studied oxide films were uniform. The values of the energy band gap were calculated from the absorption spectra, for ZnO and SiO2 samples, deposited onto quartz substrates. By calculating the average value of the refractive index in the investigated wavelength range it was found that, in general, the refractive index of the layer increased with its thickness. As a result, depending on the deposition conditions, the ZnO and SiO2 oxide films showed a good structural quality and adhesion to the substrate.

Resume : Graphene (Gr), a two-dimensional material composed of carbon atoms arranged in a honeycomb lattice, is considered an excellent candidate for fabricating transparent conductive film for optoelectronic applications [1]. High optical transparency [2], high electrical conductivity [3] chemical stability are the properties that identify graphene as a valid substitute for the indium tin oxide (ITO). Carbon dots (CDs) are a wide family of zero-dimensional (0D) carbonaceous nanoparticles with a diameter smaller than 10 nm capable of bright and tunable fluorescence [4]. Their attractive optical properties [5] combined with low cost, low toxicity, water-solubility, photo-stability and biocompatibility have attracted attentions in view of many applications such as optoelectronics [6], photocatalysis [7] and solar energy harvesting [8]. CDs-Gr composites, joining the main properties of CDs, such as optical activity, and Gr, such as high conductivity and transparency, can pave the way to new all-carbon optoelectronic devices. For these applications, the CDs-Gr composites have to be deposited in the form of 2D solid systems, and their interface and surface properties have to be carefully evaluated in order to tailor their optoelectronic behavior [9]. In this work, the structural and optical properties of CDs deposited on Gr/SiO2/Si substrate are thoroughly investigated. In particular, a systematic micro-photoluminescence analysis, employing different excitation lasers from green to blue, shows that CDs maintain their emission tunability, but there is a reduction in the emission efficiency of the CDs in presence of Gr. The different electrical properties of Gr and SiO2, conductive the first and insulating the second, suggest the possibility of a photo-induced electron transfer between CDs and Gr. [1] F. Bonaccorso et al., Nature Photonics, 2010, 4, 611 [2] R.R. Nair et al., Science, 2008, 320, 1308 [3] X. Du et al., Nat. Nanotechnology, 2008, 3, 491 [4] Ya-Ping sun et al., J. Am. Chem. Soc., 2006, 128, 7756 [5] A. Sciortino et al., Phys. Chem. Chem., Phys. 2017, 19, 22670 [6] L. Xiaoming et al., Adv. Funct. Mater., 2015, 25, 4929 [7] X. Zeng et al., Appl. Catal. B Environ., 2017, 202, 33. [8] P. Mirtchev et al., J. Mater. Chem., 2012, 22, 1265. [9] G. Faggio et al., Phys. Status Solidi A, 2019, 1800559

Resume : Aluminum films prepared by DC pulsed magnetron sputtering in a mixed atmosphere of argon and nitrogen exhibit two different types of morphologies depending on the N2/Ar ratio. Reflective Al is characteristic by a compact bulk-like structure and surface roughness linearly increasing with film thickness. Incident light (wavelength range from 190 nm to 1200 nm) is scattered into multiple directions however the total diffusion reflectance falls into range of 65 – 85% depending on the film thickness and wavelength of the incident light. Contrary to reflective Al, black Al films’ morphology resembles cauliflower/moth-eye structures. Such a surface is characteristic by a high light absorbance of 96 % and higher. Atomic force microscopy and transmission electron microscopy measurements showed a porous structure of black Al with pore sizes of ~10 nm and smaller. Positron lifetime spectroscopy measurements revealed an increased concentration of vacancy-like defects (mono-, di- vacancies, vacancy clusters) in black Al films compared to reflective Al films. In addition to vacancy-like defects black Al contains nano-cavities as observed by 3-gamma ortho-positronium annihilation. Applying the Tao-Eldrup model we estimated the mean size of nano-cavities to 5 A.

Resume : Nowadays there is an open challenge to obtain lead-free piezoelectric ceramics and trying to replace the PZT ceramics into energy harvesting applications. Perovskite materials have drawn great interest of researcher in this area. Nano lead-free piezoelectric BCZT Ba(Ti1-xZrx)O3-(Ba1-yCay)TiO3 (x=0.3;0.5 y=0.3;0.5) material was obtained through a hydrothermal process with controlled stoichiometry, this synthesis process will be scale-up in order to demonstrate operational reliability and recyclability. Nanostructured perovskite material denoted as BCZT was synthetized in one step process by hydrothermal method starting from soluble salts. KOH was used as mineralizer. The amounts of Ba(OH)*8H2O, Ca(NO3)2 · 4H2O, TiCl4 and ZrCl4 were weighed in agreement with the theoretical molar formula Ba(Ti1-xZrx)O3-(Ba1-yCay)TiO3 (x=0.3;0.5 y=0.3;0.5). The suspension was transferred to a Teflon vessel of an autoclave (5l, Berghof, Germany) with cooling system, for hydrothermal treatment at 40 at. and 473 K, for 2 h. Pressure was created inside the reaction system using argon gas. After the hydrothermal synthesis, the wet precipitate was subjected to spray drier in order to obtain spherical grain. Chemical composition was determined by inductively coupled plasma atomic emission spectroscopy (ICP-OES) technique. The microstructure of the powders was examined by using XRD analysis, morphology of the sample was investigated by SEM. The thermal behavior of the processed samples under non isothermal regime was investigated by simultaneous differential scanning calorimetry (DSC) and thermogravimetry (TG). Acknowledgement: FAST and Nano-Enabled SMART Materials, Structures and Systems for Energy Harvesting (FAST-SMART); EU H2020 Grant 862289.

Resume : The photovoltaic technology based on perovskite as absorber has received a lot of attention due to its potential for being a low-cost effective and high-efficiency technology to produce energy at large scale. In order to favour the charge extraction, hole-transport materials (HTMs) prepared on an n-i-p architecture has to be electronically and physically compatible with the perovskite film, while maintaining a low cost. The family of perylene diimides (PDIs) has received significant attention as dyes and charge selective semiconductors in electro-optical devices, due to its tuneable electronic properties and high stability. To explore new HTMs based on PDIs, we have selected and prepared 1.6 and 1.7 isomers of dipiperidin-N-yl PDIs which suggest good compatibility with perovskite after DFT simulations. As a proof of concept, we fabricate solar cell devices applying a very thin film of the PDIs as HTM. Unlike the reference device using Spiro-OMeTAD, we noted that PDIs does not require doping of external materials to have a good performance. This, along with an improved long-term device stability, demonstrate a good potential of PDIs to be used as HTMs, open the possibility of further investigation and optimization for its use in solar cells.

Resume : In recent years, graphene has attracted great interest in different research fields while its electronic and optical properties have been intensively studied in view of several applications, in particular as transparent conductive electrode (TCE). Handling these 2D, atomic thickness films has proved an arduous task requiring the development of novel technologies. In this framework, it is extremely useful to be capable to fabricate and handle membranes composed of single or multi-layer graphene completed with metallic contacts of arbitrary geometry. This gives the possibility to transfer in a single step the contacted graphene on the target substrate using the cyclododecane supported technique invented by the authors. The main advantage of the technique is the possibility to obtain a novel TCE/metal-grid integrated structure, especially applicable in the photovoltaic field, which allows to avoid any further substrate process after the transfer of graphene. To test this concept, in the present work we have realized Graphene/Gold-grid membranes and transferred them on c-Si substrates in order to obtain Schottky barrier solar cells. The cell efficiency at 1 Sun illumination for a device with 4cm2 active area is 7.1%. The experiment can be extended to graphene membranes with grids made of other metals, such as Aluminium.

Resume : Graphene-based Schottky-junctions offer a new interesting platform for photovoltaic devices, and Schottky-junction solar cells are intensively investigated with the aim to improve their performance. Recently, Schottky junction solar cells were fabricated by using a single layer of graphene as a metal. In this work, we propose a graphene/InP thin-film Schottky-junction solar cells by using a plasmonic structure. The graphene/InP thin film solar cell was designed with a periodic array of plasmonic back-reflector and Indium tin oxide (ITO) as an anti-reflection coating layer on top of the solar cell. 3D-simulations were carried out based on a finite difference method (FDM) method to determine absorption, the weighted absorption and the short-circuit current. The optimized design of the solar-cell structure, reached a maximum short-circuit current density and optical absorption of 33.01 mA/cm2 and 0.985 (98.5%), respectively under AM1.5G solar irradiation. The optimized design demonstrates a considerable reduction in absorbing layer thickness respect to the planar InP-based solar cell.

Resume : Al-doped ZnO is one of the most considered transparent conductive oxides (TCOs) as an alternative to the most commonly used Indium Tin Oxide (ITO), whose replacement is desirable to reduce the use of the critical indium element. In this work, Al-doped ZnO thin films were deposited using a RF magnetron sputtering system in Ar atmosphere by two distinct targets (ZnO and Al), where the Al percentage was varied changing the power ratio between the two targets from 0.1 to 0.7. Plasma emission spectroscopy during the deposition process showed the presence of Zn+, Zn, Al and O emission lines. The Zn and Al concentrations in the plasma can be calculated and correlated to the Al:ZnO thin films properties. Process optimization and technical improvements of the equipment were adopted to gain repeatability, accuracy and a better control of the systematic errors. X-ray diffraction (XRD) measurements were conducted to identify the microstructural modifications when varying the Al content in the films. X-ray photoelectron spectroscopy (XPS) analyses on the AZO films gave the binding energies of Zn 2p3/2 and 2p1/2 that are centered at 1021.6 and 1044.7 eV, respectively. No energy shift in the Zn 2p states is observed. The O 1s peak is asymmetric and can be resolved into two components, P1 at 530.2 eV and P2 at 531.6 eV. Peak P1 can be attributed to O2- ions surrounded by Zn2+, indicating Zn–O bonds; Peak P2 can be associated with O2-ions in the oxygen-deficient regions within the matrix of ZnO. The electrical conductivity and Seebeck coefficient were measured in standard Van der Pauw configuration, and their values are comparable with the literature.

Resume : Multiferroics are materials possessing different ‘ferroic’ orders such as ferro-magnetism, ferro-electricity, ferro-elasticity etc. Many rare earth ortho-chromates and ferrites were reported to exhibit multiferroic properties and magneto-electric coupling. It was reported that in many of the rare earth chromates, the onset of polar ordering appears at temperatures slightly higher than their antiferromagnetic ordering. Here we investigate the temperature evolution of structural and dielectric properties of Holmium based ortho-chromate, HoCrO3. Polycrystalline HoCrO3 was prepared by conventional solid state synthesis route. Temperature variation of Synchrotron X-ray diffraction was done at Photon Factory Japan using a 300mm Debye-Scherrer diffractometer on the B12 beamline. Rietveld refinement of crystal structure at various temperatures was carried out using FullProf suit software. Magnetic measurement was done using SQUID-VSM (Quantum Design) and Dielectric spectroscopy measurements were carried using Broadband Dielectric/Impedance Spectrometer, Novocontrol technologies. Reitveld refinement of the synchrotron x-ray diffractogram at room temperature confirms the perovskite orthorhombic structure crystallizing in the Pbnm space group. Temperature evolution of synchrotron x-ray diffraction points to the presence of variation in unit cell volume around 240 K and 100 K. Magnetic measurement confirms the antiferromagnetic transition at 140 K. The compound exhibits a dielectric constant of 19.46 at 1.784 kHz at room temperature. Also, temperature variation of the real part of the dielectric constant reveals a typical relaxor like behavior with low temperature and high temperature plateaus along with two anomalies at 240 K and 140 K. Analysis of peaks in the loss tangent curves confirms thermally activated dielectric relaxation. The dielectric anomaly at 140 K indicates a possibility for magneto-electric coupling in the material. However, the peak at 240 K corroborates the volume change observed in synchrotron analysis which is associated with a possible structural transition (Pbnm to Pna21), usually observed in similar rare earth based ortho-chromates having ferroelectric ordering. In the present work synchrotron x-ray diffraction technique was used for the first time to confirm the structural transition in HoCrO3. Our structural as well dielectric studies proves HoCrO3 as a multiferroic material with magneto-electric coupling.

Resume : Because of high energy and power density, Li-Ion batteries (LIB) are the predominant energy storage technology to power mobile electronics and electric mobilities. The needs for higher energy is ever-increasing and one option to store sufficient amounts of energy is stacking multiple electrodes into one cell. The battery is constructed by battery electrodes consist of Cu foils coated with the anode material and Al foils coated with the cathode material, and separator soaked in electrolyte. While the Cu, Al, and separator are essential for the battery operation, they are inactive components that do not store energy. Increasing the thickness of the active material coating will decrease the relative fraction of this dead volume. Unfortunately, producing thick electrodes is challenging because of cracking and flaking during drying, and further, both the electron and Li-ion transport are poor through thick layers. In this presentation, we will discuss key performance differences between conventional electrodes and bi-continuous electrodes and offer our explanation to the improved areal capacity and rate performance.

Resume : Transition metal nitrides possess high thermal stability, high hardness, good tribological properties. Among them, some nitrides, such as zirconium nitride, excel in their optical and electrical properties, making them a suitable material for plasmonic applications. In this work, we deal with a study of the growth process of zirconium nitride (ZrNx) films by means of RF magnetron sputtering of Ti target in a reactive nitrogen ambient. The resulting structure and corresponding plasmonic properties of ZrNx coatings are very sensitive to some deposition parameters, especially, the composition of Ar/N2 gas mixture. Different chemical compositions, such as ZrN, Zr2N, Zr3N4, and ZrN2, can be obtained via the control of the sputtering reactive gas mixture that leads to different physical properties of the resulting zirconium nitride film. The films are grown on fused silica, silicon and MgO substrates at a substrate temperature ranging from 20°C to 500°C. The growth process is monitored using an in-situ spectral ellipsometer in a spectral range from 245 to 1690 nm. The ellipsometric data are analyzed using mathematical models based on Drude-Lorentz oscillators. A number of physical parameters, such as free-electron concentration, Drude relaxation time and electrical resistivity, are estimated at each stage of the deposition process by proper analysis of dielectric functions. Special attention is paid to the initial stage of growth when the free-electron behavior is significantly influenced by the interface between the substrate and the ZrNx film. The obtained results are compared and discussed with those obtained by Van der Pauw and Hall effect measurement. The crystallinity and surface morphology were analyzed by X-ray Diffraction method (XRD) and Atomic Force Microscopy (AFM).

Resume : Our work has allowed us to clarify the relations structures / properties and the isomerization reactions of icosadeca-ene. As regards the relations structures / properties, our results are: 1- The study of the conduction properties of icosadeca-ene doped with iodine gas at saturation as a function of various parameters regulating morphology and density of the material was optimized. In particular we have shown that the two key parameters governing the electrical conductivity of the polymer are the density and the fibrillar structure of icosadeca-ene. 2- The comparison of samples prepared horizontally and vertically gave a conductivity of greater than ~ 45 % for those deposited vertically, thereby reflecting the difference in morphology of the two types of film.. 3- The study of the ohmic conductivity of undoped and thermally isomerized samples showed a very different behavior depending on whether the icosadeca-ene film is deposited horizontally or vertically, thus confirming the different morphologies of the analyzed films. With regard to isomerization reactions of icosadeca-ene, our results are: i- The study of the thermal isomerization Cis / Trans of undoped icosadeca-ene by differential thermal analysis allowed us to calculate the activation energy of the reaction Ea=30.57 kcal/M, as well as the pre-exponential factor A = 3.7*1014 /s regardless of the type of polymer considered (deposited vertically or horizontally). ii- The kinetic studies by DSC showed that the isomerization reaction was neither of order 1, nor of a simple order. iii- An additional study of the thermal isomerization was carried out by Raman backscattering . This study allowed us in particular to establish a new original method for the determination of the isomeric composition of samples of icosadeca-ene. Also a relation for connecting the laser power to the induced temperature at the impact level was proposed. Finally, the kinetics of isomerization approaches the order 2/3. Note that the activation energy and the pre-exponential factor of the isomerization reaction determined by this method are different from those obtained by DSC.

Resume : The aim of this work was on the one hand the development of theoretical models ( mathematical) to numerically simulate the experimental results of variations in the electrical conductivity as a function of various parameters, and on the other hand, the study of boundary conditions necessary for the numerical resolution of the heat propagation equation. Note that all obtained theoretical models are of the linear or sigmoidal form, Boltzmann type. Most obtained models allowed finding relationships more or less simple between the different parameters with an acceptable relative error of calculation, which allowed us to calculate theoretical values very close to the experimental values for the physical variables studied. Some of our models have given incorrect values , this can be explained by the fact that our calculation method is not reliable for this kind of data (values in small intervals). Note that this type of calculation can be improved by using other interpolation methods in particular the method of cubic splines. The model we have developed for solving the heat propagation equation, can serve in the research on the estimation of the isomerization temperature of tetradecahepta-ene by laser effect, which is widely used in current studies on the polyacetylene. Finally, it should be noted that our model for solving the heat propagation equation can be more efficient when the semi-empirical method is used to set the condition at the lower boundary of the domain.

Resume : In order to interpret the dynamic variation of thin film material during high power laser irradiation, the variation of optical constants and thickness of single layer coatings at different temperature was studied by combining the ellipsometry and the heating stage. From room temperature to 320°, the refractive index of SiO2, HfO2 and Al2O3 single layer decreases first and then increases, the thickness of these layers increases first and then decreases. But their inflection point occurred at different temperature, and the amount of change was also different for the layer with different material. Thermal expansion and water evaporation processes were applied to explain the temperature dependent properties of the dielectric coatings. The thermal damage and thermal distortion under high energy laser irradiation was interpreted from the view of optical property variation of the material, this will probably lead to a better understanding of the physical principles behind the laser-matter interaction.

Resume : Mechanochemical treatment of waste materials is a powerful tool for pollution remediation and waste management. Mechanochemistry is defined to describe the chemical and physicochemical transformations of materials as a result of the mechanical energy input. On the other hand mechanochemical activation is a possibility to obtain products in a metastable state which increase their chemical activity. Four Fe–based amorphous alloys containing critical raw materials (CRM) were treated in a high-energy planetary ball mill at different conditions. The exact chemical compositions of studied materials are: Fe81B13.5Si3.5C2, Fe78B15Mo2Si5, Fe67B14Co18Si, and Fe40B16Ni40Mo4. The aim of the study is to investigate the appropriate conditions of mechanochemical processing of these materials to obtain partial crystallisation and formation of nanocrystals in the amorphous ribbon structure. The as-prepared active materials have higher specific surface area, which is also of great importance for their reuse for dye-contaminated wastewaters remediation. Characterisation of the bulk and the surface of initial and MC treated samples was done using powder X-ray diffraction (XRD), RT and LNT Mössbauer spectroscopy (MS), as well as conversion electron MS. Acknowledgements: The authors gratefully acknowledge the financial support of the Bulgarian National Science Fund at the Ministry of Education and Science - Project № КП-06-КОСТ/18/ 2019.

Resume : Last decades, scientific interest has been attracted for electrochromic coatings, since these are essential in a variety of novel technological applications such as switches, batteries and smart windows. Tungsten trioxide is one of the most common electrochromic film for smart window applications that can be used in order to reduce the energy consumption on buildings. To date many methods, such as sol-gel, hydrothermal synthesis, chemical vapour deposition (CVD) and magnetron sputtering, have been used for the deposition of WO3 layers. As has been shown, one very important parameter for the response of the layers is their morphology. In this work, amorphous WO3 coatings were grown on indium tin dioxide glass substrates using magnetron sputtering with tungsten target and various amount of vacuum in the deposition chamber. The coatings were characterized by X-ray diffraction, XPS, UV-Vis-IR spectroscopy, scanning electron microscopy and cyclic voltammetry in order to investigate the importance of their porosity in the improvement of their electrochromic performance, including durability, time response, charge density and coloration efficiency.

Resume : There is a growing concern worldwide about securing access to metals and minerals needed for economic production. This study offers a survey of critical raw materials (CRMs) used in energy, optoelectronics, transportation and machinery manufacturing. Understanding of the role of CRMs and a careful evaluation of environmental and health impacts are key factors in materials’ substitution, when searching for alternatives able to maintain the performance of components and products. The CRMs issue is analysed considering main actors: Europe, Japan, United States and China.

Resume : After Indium was included in critical raw material coverage by the European Union, researchers have recently begun to show interest in the synthesis and characterization of In-free multi-functional materials. For these materials to be used in areas where indium is used, such as optoelectronic applications, it should show similar properties with indium [1]. Therefore, structural and optical characterizations which are effect their usability in that kind of application are very important. In this context, it can be said that II-VI semiconducting materials such as MgO and CdO exhibit similar structural and optical properties compared with the Indium doped tin oxide. However, among these multifunctional semiconducting materials ZnO steps forward due to its unique properties such as wide bandgap, large exciton binding energy, high chemical stability, and usability in environment-friendly applications [2,3]. Also, these unique properties of ZnO can be altered by both growth technique and external doping [4]. Among the rare earth metals, Nd is one of the elements commonly used in high power laser applications, as well as the reduction of the optical band spacing of ZnO as a result of the substitution of Nd3+ ions into the ZnO crystal structure, makes ZnO useful for applications like photocatalytic applications [5]. Similarly, in this study neodymium-doped ZnO thin films were grown by simple chemical spray pyrolysis technique in the Nd range of 0 – 5 at.% to investigate its usability in optoelectronic applications. For this aim, XRD and UV-Vis-NIR spectroscopy measurements were conducted. According to XRD analysis, the Nd-doped ZnO films have been exhibited a smooth, dense, and wurtzite phase. Also, the results showed that with the variable Nd doping concentration, the films can be adjusted to have semiconductor properties with good optical transmittance in the visible range. All results and variations in structural and optical properties of ZnO films as a function of Nd doping have been correlated and discussed in detail. References [1] Aydogan, S., & Yilmaz, M. (2019). Crystallographic disorders depending on monovalent cations addition and their effects on ZnO's characteristics. Ceramics International. [2] Rani, T. D., Tamilarasan, K., Elangovan, E., Leela, S., Ramamurthi, K., Thangaraj, K., ... & Liebig, A. (2015). Structural and optical studies on Nd doped ZnO thin films. Superlattices and Microstructures, 77, 325-332. [3] Subramanian, M., Thakur, P., Gautam, S., Chae, K. H., Tanemura, M., Hihara, T., ... & Jayavel, R. (2009). Investigations on the structural, optical and electronic properties of Nd doped ZnO thin films. Journal of Physics D: Applied Physics, 42(10), 105410. [4] Yilmaz, M. (2019). A function of external doping: Characteristics of inorganic nanostructure based diode. Ceramics International, 45(1), 665-673. [5] Kumar, S., & Sahare, P. D. (2012). Nd-doped ZnO as a multifunctional nanomaterial. Journal of rare earths, 30(8), 761-768.

Resume : Global energy shortage and greenhouse gas emissions caused by fossil fuels mean that clean, sustainable, and renewable energy is necessary. Waste is another concern, with electronic waste gaining importance due to the growing global consumption of electronic devices that are difficult to recycle due to the complex and hazardous nature of electronic materials. The study here presented aimed at tackling both issues at the same time: the valorization of e-waste to produce a bi-functional nanomaterial for both energy storage and energy harvesting applications. The bi-functional nanomaterial, with an overall thickness around 150 nm, consists of a two-step electrodeposited three-layered copper oxide with different oxidation states (0, 1, and 2) to enhance efficiency which can act as (a) a supercapacitor material for energy storage, and (b) photo-electrocatalyst for solar water splitting. As prepared (i.e., before thermal treatment), the film behaves as a supercapacitor with a capacitance of 106 F.g-1. Low-temperature heat treatment can then transform the film into a photo-electrocatalyst delivering a photocurrent of up to 2.3 mA.cm-1, demonstrating that the functionality of the bi-functional nanofilms can be tuned by varying the ratio of oxidation states of Cu in the film through the heat treatment. EIS results revealed that the electron-hole activity of the film differed substantially in the presence of the light, although the copper oxide film can also experience low stability in certain conditions. Keywords: photocatalyst, water splitting, supercapacitor, renewable energy, sustainability, recycling of electronic waste, nano thin film, electrochemical synthesis

Resume : Thermoelectric (TE) is the promising technology for waste heat recovery and the performance of TE devices is given by figure-of-merit, ZT=(S^2 ?T)??, where, S, ?, T & ? stands for Seebeck coefficient, electrical conductivity, absolute temperature & total thermal conductivity, respectively. The combined term S^2 ? describes the power factor (?) which represents the electronic part in TE performance. Half-Heusler (HH) alloys lead the promising class of materials for several applications such as thermoelectrics, magnetism, spintronic. Among HHs, ZrNiSn is widely studied for its thermoelectric properties. Bodak et al.1 show the low-temperature electronic transport and magnetic properties of Mn-doped ZrNiSn. Here, we have investigated the effect of Mn-doping on the electronic transport properties of ZrNiSn for high temperature (room temperature to ~873 K). The ZrNi1-xMnxSn (x=0-0.04) samples were prepared via Arc Melting and then consolidated by using Spark Plasma Sintering. The desired half-Heusler phase for all the synthesized samples was confirmed by the X-ray diffraction technique. Further, the samples were characterized for thermoelectric properties. The electrical conductivity increases with temperature which is corresponding to the semiconducting behavior. At high temperature ~873 K, electrical conductivity was realized to be decreased in Mn-doped ZrNiSn and Seebeck coefficient shows marginal variation compared to pristine ZrNiSn. The power factor of 3.53 mW-1K-2 at ~873 K was realized in pristine ZrNiSn HH which was found to be decreased in Mn-doped ZrNiSn HHs. Reference: 1. Bodak, O.; Padlyak, B.; Stadnyk, Y. V.; Pierre, J.; Tkachuk, A.; Romaka, L.; Gorelenko, Y. K., Synthesis, crystal structure and physical properties of ZrNiSn semiconductor doped with Mn. Journal of alloys and compounds 2001, 317, 357-362.

Resume : The Hydrometallurgical processing of nickel metal hydride (NiMH batteries) generates a feed containing several REEs. In the majority of the developed processes, REEs are recovered as a mixture. To increase their potential, the utilization of this mixture should be explored. Otherwise, the demand for individual separation of REEs will limit the feasibility of current technologies. Here, the reuse of the outputs generated by recycling for synthesis of new magnetocaloric materials has been investigated. The outputs utilized was a rare earth element-rich product. After removing some impurities from this feed, especially aluminium, we have used the obtained product in the manufacturing of advanced REEs-based magnetocaloric materials for magnetic refrigeration especially manganites. The X-ray diffraction analysis shows that the magnetocaloric samples are well crystallized with presence of secondary phases REE-oxide and Mn2O3. We have studied the magnetic and magnetocaloric effect properties of the obtained samples.

Resume : Indium Tin Oxide (ITO) is a unique material with optical and electrical characteristics that make it the material of choice in many applications such as displays, touch screens, solar cells and optoelectronic devices. ITO main constituent (about 78 wt%) is In, a by-product of Zn metal, which is subjected to large price oscillations and has been listed recently among he critical raw materials (CRMs) for EU. In this work the report on the effect of growth parameters on the optical and electrical properties of highly transparent and conductive Al-doped zinc oxide (AZO) single layer films and AZO/Ag/AZO multilayers fabricated by radio frequency sputtering. The electrical and optical properties of the films were investigated as a function of the growth parameters (substrate temperature, radio frequency power, working pressure and oxygen partial pressure). High transmittance (up to 91%) and low sheet resistance (down to 33 Ohm/square) were measured for AZO films, while lower transmittance up to 83% and lower sheet resistance down to 15 Ohm/square for Ag/AZO multilayers. The goodness of the TCOs was evaluated basing on the optical and electrical properties by using the Haacke’s figure of merit.

Resume : Stationary electrical storage applications needed to power utility grids and industrial sites require battery packs that have the ability to combine high power, high capacity, and long cycle life. In addition, battery systems for stationary application are expected to have optimal sustainability across the entire supply chain, including the replacement of essential raw materials. In fact, the materials needed for the construction of the current generation lithium-ion batteries, such as cobalt, nickel or manganese, may not be available enough to meet the demand for large-scale applications. The interest in next-generation Li-ion and non-Li-ion batteries is growing, and among these lithium-sulphur batteries represent a promising challenge due to the low cost and high availability of sulphur. However, the use of lithium metal places some limits related to the safety of the device. One possibility to decrease the risk associated with the use of lithium metal is to reduce or eliminate liquid electrolyte with the result of an increase in the safety of the devices. in this work we propose the use of gelled electrolytes for the realization of lithium-sulphur batteries with high capacity and safe use. The results obtained in the realization of a lithium-sulphur battery with a polymeric solid electrolyte based on PEO gelled with low weight polyether will be presented.

Resume : The need for high performance materials for high temperature applications and severe harsh conditions is a major challenge in the roadmap towards a circular economy by the SETPLAN. The advances from the H2020 project NEXTOWER provide some inputs on the materials technologies and the design for maintenance strategies that could be deployed to produce components with longer service life in applications such as concentrated solar power (CSP) and CO2 - technology. Starting from results achieved on high temperature liquid lead environment of special layered metal systems, a general perspective is drawn for cross-cutting applications where partial substitution and better OPEX can be pursued.