The thin film approach for Solid Oxide Cell (SOC) electrolytes offers a pathway to reduce the high fabrication and operating temperatures of these devices. In this work, we present a detailed ex situ and in situ study of 8 mol% yttria-stabilized zirconia (8YSZ) nanostructured dense thin films with a thickness of 100 nm. These films were synthesised through the sol-gel method and deposited by dip-coating on fused glass. The microstructural and crystalline evolution in the 300-800 degrees C range was studied by synchrotron Grazing Incidence X-ray Diffraction (GIXRD). Crystallisation of the 8YSZ films was observed to start at 343 degrees C with 4-5 nm crystallites consisting only of the cubic phase. With increasing temperature, this phase is maintained and the crystallite size reaches 38 nm at 800 degrees C. Additionally, the evolution of the lattice parameter was studied, which allowed us to determine the variation of the thermal expansion coefficient (TEC) of the films during both heating and cooling. The TEC as a function of temperature has three linear regions during heating and two during cooling, with values between 9.6 x 10-7 K-1 and 3.7 x 10-5 K-1. These findings provide valuable insights into the structural response of the material under thermal cycling, relevant to the performance and stability of SOC devices. Coupled with the crystallographic characterisation, the electrical properties of the thin films were studied through conductivity measurements, obtaining conductivities about 1.5 to 5 times higher than the conductivity of 8YSZ bulk samples, with values of 0.06 S cm-1 at 700 degrees C. Thus, the conjunction of a reduced electrolyte thickness with the enhanced conductivity of nanostructured 8YSZ makes these films attractive for intermediate-temperature SOC applications.

The nuclear and magnetic structure of the spinel MnCr2O4 is reinvestigated by magnetization, specific heat, and neutron diffraction experiments at different temperatures. Four samples of this spinel synthesized under different atmospheres are analyzed. Through these experiments, a new magnetic phase, with propagation vector k ⠂I2 = (0.6597(1) 0.5999(1) 0.1996(2)), not previously reported, is identified below 18 K when the sample is synthesized under a reductive atmosphere. A possible explanation for the different magnetic ground states observed is given based on the competition among the main exchange interactions present in the system. Using the magnetic superspace group formalism, the symmetry of the nuclear and magnetic structures is determined. The presence of transverse conical magnetic structures in the lower-temperature phases allows for multiferroicity in this compound, and the electric polarization direction is determined for each magnetic phase.

Nowadays, chromium-based normal spinel oxides ACr2O4 are one of the most studied materials in the condensed matter community due to the interplay between its magnetic, electric and structural properties [1,2].In particular, for MnCr2O4, the ground state magnetic structure is still controversial because the magnetic structures reported by different groups and investigated by independent techniques are inconsistent [1-3].

This work presents the structural and electrical characterization of K2NiF4-type layered perovskites of LaSrAl1−xMgxO4−δ composition to be used as oxide–ion electrolytes for a solid-oxide fuel cell (SOFC). These perovskites were prepared by mechano-chemical synthesis (ball milling), an alternative to traditional synthesis methods such as citrate-nitrates and solid-state reaction. With these methods, two things are avoided: first, the use of nitrate salts, which are more environmentally harmful than oxide precursors, and second, it saves the series of long thermal treatments associated with solid-state reactions. After grinding the precursors, nanometric particles were obtained with a combination of crystalline regions and amorphous regions; this effect was determined by XRD and TEM, showing that Mg has a positive effect on the phase formation by only mechanical synthesis. R2C4: After sintering, it was found by XRD that the sample x = 0.1 only presents the diffraction peaks corresponding to the desired phase, which shows a phase purity greater than 97%, even higher than that of the standard undoped sample. For x = 0.2 and 0.3, there was a segregation of impurities, possibly by the local migration of La and Sr heavy cations; this was determined by SEM and EDS. The electrical characterization of the sintered pellets was carried out by electrochemical impedance spectroscopy, which determined that the incorporation of Mg in the structure improves the ionic conductivity by three orders of magnitude, obtaining conductivities of 1.6 mS/cm at 900 °C for x = 0.2. Although the improvement in conductivity is considerable, many challenges such as densification, the segregation of impurities, and the study of mechanical and thermal properties must be carried out on these materials to endorse them as solid electrolytes in SOFC.

A Co-free perovskite material, La0.7Sr0.3Cu0.15Fe0.85O3-6, is synthesized and electrochemically characterized to evaluate its potential application as electrocatalyst in the air electrode of solid oxide cells. The powder was firstly synthesized by the sol-gel method and subsequently morphologically and structurally characterized by scanning electron microscope and X-ray diffraction. Symmetrical circular button cells featuring Sm-doped ceria (20% Sm) as supporting electrolyte and La0.7Sr0.3Cu0.15Fe0.85O3-6 as electrocatalyst were manufactured to carry out elec-trochemical investigations. Two different electrode morphologies are analyzed. In the first structure, the La0.7Sr0.3Cu0.15Fe0.85O3-6 calcined powders are directly deposited by slurry coating on a dense sintered sup-porting pellet of Sm-doped ceria. In the second electrode configuration, the precursor solution of La0.7Sr0.3-Cu0.15Fe0.85O3-6 impregnates a porous scaffold of Sm-doped ceria, previously deposited and co-sintered with the supporting electrolyte. The performance of the samples was studied by means of electrochemical impedance spectroscopy, measuring polarization resistances of 0.0153 & omega;& BULL;cm2 at 700 degrees C and 0.052 & omega;& BULL;cm2 at 600 degrees C for the slurry coated and infiltrated electrodes, respectively. These values, according to the authors knowledge, are amongst the lowest ever obtained for Co-free solid oxides electrodes. However, the very high electrocatalytic activity obtained at intermediate temperatures is not accompanied by chemical stability over time.

Co-free REBa2Cu3O6+ẟ (RE= La, Nd, Sm, Gd and Y) triple perovskite ceramics prepared by auto-combustion were systematically studied as cathodes for intermediate-temperature solid oxide fuel cells. The orthorhombic to tetragonal phase transition typical of these compounds was studied, and its relation with electrochemical performance due to oxygen vacancy ordering variations was assessed as neutral. The model that best fits the electrochemical impedance spectroscopy data obtained for symmetrical cells prepared on 10% gadolinia-doped ceria (GDC, Gd0.1Ce0.9O1.95) electrolyte pellets indicates an oxygen diffusion/incorporation co-limited process is the rate-limiting step of the oxygen reduction reaction (ORR). A maximum power density of 425 mW.cm  2 was obtained for the YBa2Cu3O6+ẟ material deposited by screen-printing on a commercial half-cell with 8YSZ-Ni anode and 8YSZ electrolyte coated with a GDC barrier layer. A clear correlation is observed between the power density and ionic radii of the RE cation of these triple perovskites.

NASICON-structured glass-ceramics based on the Li1+xCrxGeTi1-x (PO4)(3) (0 <= x <= 1) system are synthesized by the melt-quenching method followed by glass crystallization. Since Ti4+ and Cr3+ have approximately the same crystal radius in octahedral coordination, this aliovalent substitution should avoid considerable changes in the cell volume, thus allowing us to evaluate the true contribution of the substitution of a tetravalent cation by a trivalent one on other structural factors. The crystal structure of these glass- ceramics is investigated by X-ray and high-resolution neutron diffraction while the electrical properties are accessed by impedance spectroscopy. Fourier differences and bond valence energy landscape analyses are used to determine the additional Li position and occupancies caused by the aliovalent substitution of Ti4+ by Cr3+. The most important change in the structural features caused by the increase in the lithium content in the chemical formula is the occupation of the 36f position followed by the partial depopulation of the 6b sites. Furthermore, the grain-related ionic conductivity and activation energy for lithium conduction are notably dependent on the aliovalent substitution. The correlations between these two main findings are discussed herein.

The BCZY perovskite was studied by NDP, QENS and TOF-SIMS techniques, focusing on the application of this material as a potential PC-SOFC electrolyte.

We report on the structural and electrical properties of nanocrystalline zirconium nitride films grown by reactive sputtering on Si (100) substrates at room temperature. The samples were grown with a N-2/Ar mixture varying the N-2 concentration between 8 and 60% of the total atmosphere. The films are nanocrystalline with the coexistence of conducting and insulator phases. The electrical resistivity evolves from ZrN with a metallic state to an insulating rich nitrogen phase, passing through a semiconductor-like behavior as N-2 in the mixture increases. A variable-range-hopping regime describes the temperature dependence of the resistivity for mixtures between 30 and 40%. Reactive mixtures of 50 and 60% of N-2 give more insulator films. Beyond these macroscopic properties, the films display inhomogeneity electrical properties at the nanoscale with coexistence regions of different conductivity. The inhomogeneities reduce as nitrogen stoichiometry increases and the films become more insulators. Our results are relevant for applications including conducting electrodes and insulator barriers in tunneling devices.

The potential of calcium-doped layered perovskite compounds, BaNd1–xCaxInO4–x/2 (where x is the excess Ca content), as protonic conductors was experimentally investigated. The acceptor-doped ceramics exhibit improved total conductivities that were 1–2 orders of magnitude higher than those of the pristine material, BaNdInO4. The highest total conductivity of 2.6 × 10–3 S cm–1 was obtained in the BaNd0.8Ca0.2InO3.90 sample at a temperature of 750 °C in air. Electrochemical impedance spectroscopy measurements of the x = 0.1 and x = 0.2 substituted samples showed higher total conductivity under humid environments than those measured in a dry environment over a large temperature range (250–750 °C). At 500 °C, the total conductivity of the 20% substituted sample in humid air (∼3% H2O) was 1.3 × 10–4 S cm–1. The incorporation of water vapor decreased the activation energies of the bulk conductivity of the BaNd0.8Ca0.2InO3.90 sample from 0.755(2) to 0.678(2) eV in air. The saturated BaNd0.8Ca0.2InO3.90 sample contained 2.2 mol % protonic defects, which caused an expansion in the lattice according to the high-temperature X-ray diffraction data. Combining the studies of the impedance behavior with four-probe DC conductivity measurements obtained in humid air, which showed a decrease in the resistance of the x = 0.2 sample, we conclude that experimental evidence indicates that BaNd1–xCaxInO4–x/2 is a fast proton conductor.

In this work, the characterization of ZrO2 thin films synthesized by the sol-gel method, using two different routes, is presented. Thin films were deposited by dip-coating on glass and Zircaloy-4 (Zry-4) substrates, and heat treated at 500 degrees C under atmospheric air. Characterization was carried out using X-Ray Diffraction (XRD), Grazing Incidence X-Ray Diffraction (GIXRD), High Temperature X-Ray Diffraction (HT-XRD), Raman Spectroscopy (RS), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Electrical properties of films were studied by conductivity measurements. These films present a thickness of 90 and 200 nm on glass, depending on the synthesis route, and consist of nanocrystals with predominantly tetragonal phase. On coated Zry-4, a non-uniform but dense ZrO2 layer without cracks grows, in contrast with the un-coated Zry-4, where a thicker layer was formed with the presence of micro-fissures. A GIXRD study showed that both tetragonal and monoclinic phases are present in the oxide layer. Conductivity measurements indicated that these films have excellent insulating properties, with resistivity values that exceed 0.5 M Omega.cm below 300 degrees C. These exceptional properties and the retention of high symmetry phases make this method very attractive for growing good electrical insulator and anti-corrosion ZrO2 thin film coatings.

This work presents a systematic study of the high temperature properties of BaCe0.4Zr0.4Pr0.2O3−δ perovskite in view of its potential application in proton conducting solid oxide fuel cells.

YBa2Cu3O6+δ (YBC) oxygen deficient perovskite was synthesized by an auto-combustion method and was studied as potential cathode for Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC). Synchrotron X-ray thermodiffraction in air shows a phase transition from orthorhombic Pmmm to tetragonal P4/mmm space groups at ~ 425 °C. The chemical compatibility with Ce0.9Gd0.1O1.95 (GDC) electrolyte was investigated in air where certain reactivity was observed above 800 °C. However, the main phase is Ba(Ce1-xYx)O3, a good ionic conductor. The catalytic performance in air was obtained by electrochemical impedance spectroscopy (EIS) measurements on YBC/GDC/YBC symmetrical cells. The area specific resistance (ASR) values change from 13.66 to 0.14 Ω cm2 between 500 and 800 °C, with activation energy (Ea) of 0.41 eV. The results suggest potential applications of YBC as IT-SOFC cathode.

Zirconia based materials possess a unique set of attractive properties, which are responsible for the many applications in which they are used [1]. Some of these involve the use of thin films, whose properties are highly dependent on synthesis and deposition methods. Major changes in the Zr-O phase diagram, thus in material properties, occur when the crystallite size is reduced down to the nanoscale. A good example is that cubic or tetragonal phases, that have better mechanical properties than the monoclinic phase, can be retained in nanocrystalline zirconia [2,3]. The addition of yttria to zirconia can also lead to the stabilization of the high symmetry phases, producing the well-known yttria stabilized zirconia (YSZ). YSZ is the most widely used electrolyte in solid oxide fuel cells (SOFC) due to its high and pure ionic conductivity above 800 °C. However, such high operation temperatures result in high degradation rate for the SOFC, which increases the cost of this technology. Different strategies have been proposed to lower the SOFC operating temperature, being one appealing approach to employ dense thin-film based electrolytes [4].

We present the diffusion pathways in perovskite-like structures. The modules of Gfourir and BondStr of Fullprof are feasible to obtain different paths in first approximation.

Oxides with proton conductivity have a great potential for applications in environmental energy technology. Despite the BaCe0.4Zr0.4Y0.2O3−δ (BCZY) perovskites being well-known proton conductors, i...

This paper address the blocking of the electronic conductivity for a BaCe0.8Pr0.2O3-delta (BCP) material due to the addition of a BaCe0.4Zr0.4Y0.2O3-delta (BCZY) thin layer. Barium cerates (BCP and BCZY) show interesting features as electrolytes for Proton Conducting Solid Oxide Fuel Cells (PC-SOFC). BCP perovskite displays good mechanical properties associated to its sintering capability, typically proposed as a possible electrolyte. However, this compound shows poor CO2 tolerance above 500 degrees C and presents mixed conductivity under wet synthetic air. Protonic transport is the main feature of BCZY perovskite and it presents an excellent CO2 tolerance. However, the drawback of this compound is its high grain boundary resistance. In this work, a BCZY film was grown by Pulsed Laser Deposition (PLD) on BCP in order to block its electronic conductivity and improve CO2 tolerance. From the electrochemical characterization of materials, it is proposed that BCP dominates transport mechanisms on the BCZY/BCP bilayer membranes under wet synthetic air and wet diluted hydrogen. Our measurements confirm that the BCZY film blocks the electronic conductivity of BCP under wet synthetic air and protects it from CO2-containig atmospheres. Due to this set of properties, the BCZY/BCP bilayer membrane represents a possible candidate as electrolyte for PC-SOFC operating between 400 and 600 degrees C. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Compounds based on barium cerates and zirconates Ba(Ce,Zr)O3−δ are oxides able to transport protons through their crystal lattice by proton hopping between oxygen sites. This feature makes them potential candidates as hydrogen sensors, membranes for hydrogen purification and isotopic exchange, and electrolyte for Proton Conducting Solid Oxide Fuel Cell (PC-SOFC) and Solid Oxide Electrolyzer Cells (PC-SOEC). Pr-doping on these family compounds decreases sintering temperature and introduces electronic conductivity. This work presents a systematic study of the high temperature properties of the BaCe0.4Zr0.4Pr0.2O3−δ (BCZP) perovskite in view of its potential use for these applications. At room temperature, BCZP presents rhombohedral structure, which transforms reversibly to cubic at 550 °C in dry air. Electrochemical measurements under dry air, wet air with water vapor (~ 2% H2O) and heavy water vapor (~ 2% D2O) were employed to describe bulk ionic and electronic transport above 200 °C. The total conductivity data exhibit behavior changes between 400 and 600 °C which could be associated to a crystal structure transition. Below 600 ºC BCZP presents low total conductivity, which limits its applications as single phase cathode material for electrochemical applications. However, the material has good thermomechanical compatibility with electrolytes (~ 11 × 10− 6 K− 1) and high CO2 tolerance (T > 900 ºC). These properties suggest that this compound could be used as oxide support for composite or impregnated electrodes, buffer layer to improve the performance of another cathode material or gas separation co-ionic membranes.

LaSrAl1−xMgxO4−δ (x = 0.0–0.3) layered perovskites were synthesized by a nitrate–citrate route followed by annealing in air at 1100 °C, and studied as potential electrolyte materials in solid oxide fuel cells (SOFCs).