X-ray diffraction (XRD) data of Dy1.2Ba1.8Fe2.1Co0.9O8-delta powder sample show that it is a single-phase oxide with a tetragonal 123-type structure (space group P4/mmm). The phase stability was verified by both XRD of quenched sample and in situ high-temperature XRD (HT-XRD) in the range of 298-1373 K, with no phase transitions detected. Transmission electron microscopy (TEM) measurements confirmed the formation of a triple-layered perovskite-related 123-type structure. Neutron powder diffraction (NPD) performed in the temperature range of 8-773 K revealed a statistical distribution of iron and cobalt ions in nonequivalent sites with pyramidal and octahedral coordination. The NPD study also confirmed a magnetic phase transition with a Neel temperature (TN) of 500 K. The magnetic structure is described by the propagation vector k = (0.5, 0.5, 0.5). The magnetic moments of iron and cobalt ions located in the octahedrally-coordinated 1d sites (mu 1d = 3.6(2) mu B at 8 K) and the pyramidally-coordinated 2 h sites (mu 2h = 3.8(2) mu B at 8 K) are coupled antiferromagnetically within the basal plane. The oxygen content of the oxide, estimated at room temperature to be 7.86, was found to decrease with increasing temperature. The linear thermal expansion curve exhibits an increase in slope with increasing temperature. The electrical conductivity shows a maximum near 1200 K.

The mass-transfer of oxygen and hydrogen between the gas phase containing humidified O2 and the La n+1Ni n O3n+1 (n = 1, 2, 3) electrode in contact with the proton-conducting La28-z W4+z O54+1.5z (LWO) electrolyte has been studied. The measurements were performed using the 18O pulse isotope exchange (PIE) technique in the temperature range of 350-800 degrees C under a flow of He + O2 in both dry and humid conditions. Electrochemical studies were carried out using electrochemical impedance spectroscopy (EIS) within the temperature range of 600-800 degrees C in humid air. The PIE study demonstrated that all La n+1Ni n O3n+1 oxides exhibit oxygen surface exchange with O2 and H2O, and the results were further justified by 1H NMR and TGA studies. The mechanism of oxygen surface exchange is discussed. EIS measurements revealed two distinct surface exchange processes for the La3Ni2O7-delta and La4Ni3O10-delta electrodes in contact with LWO, which is explained by the two-step mechanism proposed on the basis of the PIE studies. The EIS and PIE results showed that the hydration of La4Ni3O10-delta occurs through the interaction of oxygen with water on the electrode surface in a humid atmosphere, leading to the formation of hydroxyl groups and their subsequent incorporation into structural oxygen vacancies.

Using the homogenizing annealing method and X-ray powder diffraction, it was shown that in the quasi-ternary PrOx–CoO–NiO system at 1373 K in air, two series of solid solutions are formed: PrCo _1 - x NixO3 (0.0 ≤ x ≤ 0.4) with the orthorhombically distorted perovskite structure and Pr4Ni _3 - y CoyO _10 - δ (0.7 ≤ y ≤ 1.5) with the Ruddlesden–Popper type structure with n = 3. The oxygen content in both series of solid solutions is close to stoichiometric. It is assumed that Ni2+ ions are predominantly located in octahedra located in the middle of the perovskite block, while Ni3+ and Co3+ ions are in octahedra adjacent to the rock salt layers. Phase diagrams of the PrOx–CoOx and PrOx–NiO systems were constructed in “T–composition” coordinates in air using literature data.

Solid solutions Ba1-xPrxFe1-yCoyO3-δ (x = 0.3, y = 0.1-0.6 and x = 0.1-0.6, y = 0.2) with cubic structure were synthesized through a glycerol-nitrate technique. The oxygen content, thermal expansion, electrical conductivity and the Seebeck coefficient in the Ba1-xPrxFe1-yCoyO3-δ oxides were measured versus temperature in air. The oxygen content increases with increasing iron and praseodymium concentrations in Ba1-xPrxFe1-yCoyO3-δ. The value of the thermal expansion coefficient weakly depends on the composition of solid solutions. The conductivity of Ba1-xPrxFe1-yCoyO3-δ is practically independent of the concentration of 3d metals and increases significantly with increasing praseodymium content. The maximum conductivity value of 210 S/cm is obtained for Ba0.4Pr0.6Fe0.8Co0.2O3-δ at 450 °C in air. A positive value of the Seebeck coefficient indicates the predominant p-type conductivity in Ba1-xPrxFe1-yCoyO3-δ.

La2-xPrxNi1-yCuyO4+δ (x=0.5, 1, 1.5, y=0.4, 0.6, 0.8) were synthesized by a citrate-nitrate method and studied as cathode materials for IT-SOFCs by Electrochemical Impedance Spectroscopy (EIS) in symmetrical cells based on the Ce0.8Sm0.2O2-δ (SDC) and La28-zW4+zO54+1.5z (z = 0.85, LWO) electrolytes. Phase identification and crystal structure analysis by means of X-ray powder diffraction (XRPD) shows that solubility of copper y decreases with the increase in praseodymium content x due to increasing structural distortions. Thermodynamic stability of La2-xPrxNi1-yCuyO4+δ at intermediate temperatures in air tends to decrease with praseodymium doping level x and increases with copper substitution for nickel y. Oxides with x=0.5 and 0.6≤y≤0.8 are shown to be thermodynamically stable at 700 °C in air. Electrochemical performance of the La2-xPrxNi1-yCuyO4+δ electrodes improves with praseodymium and copper doping. The results of EIS measurements at different temperatures and oxygen partial pressures (P(O2)) reveal that the rate-determining step of the overall electrochemical process is charge transfer, which can be a combination of surface diffusion and bulk diffusion. EIS studies in dry and wet air indicate the presence of proton conduction in the studied electrodes. The area-specific resistances (ASRs) for La2-xPrxNi1-yCuyO4+δ with x=0.5, y=0.6 and y=0.8 in contact with SDC are comparable with those reported for Pr2NiO4+δ and equal to 0.07 and 0.065 Ω cm2 at 800 °C.

The phase relationships in the quasi-quaternary system GdCoO3–SrCoO3–δ–SrFeO3–δ–GdFeO3 at 1373 K in air have been studied. The homogeneity ranges and crystal structure of solid solutions with overall composition Gd1–xSrxCo1–yFeyO3–δ have been determined. Depending on the concentration of introduced strontium and iron, the Gd1–xSrxCo1–yFeyO3–δ oxides crystallize in orthorhombic (x = 0.1 and 0.4 ≤ y ≤ 1.0; x = 0.2 and y = 0.9, space group Pbnm), tetragonal (0.6 ≤ x ≤ 0.8 and 0.1 ≤ y ≤ 0.5, space group I4/mmm) or cubic (x = 0.9 and 0.1 ≤ y ≤ 0.9; 0.6 ≤ x ≤ 0.8 and 0.6 ≤ y ≤ 0.9, space group Pm 3 m) perovskite structure. Structural parameters were determined for all single-phase samples. It was found that an increase in the concentration of strontium and iron leads to an increase in the unit cells parameters of the Gd1–xSrxCo1–yFeyO3–δ oxides. It has been shown that the oxygen content in the Gd1–xSrxCo0.3Fe0.7O3–δ oxides, determined by thermogravimetric analysis, decreases with increasing temperature and strontium content. An isobaric-isothermal phase diagram for the GdCoO3–SrCoO3–δ–SrFeO3–δ–GdFeO3 system at 1373 K in air was constructed.

Solid solutions Ba 1- x Pr x Fe 1- y Co y O 3-delta ( x = 0.3, y = 0.1-0.6 and x = 0.1-0.6, y = 0.2) with cubic structure were synthesized through a glycerol-nitrate technique. The oxygen content, thermal expansion, electrical conductivity and the Seebeck coefficient in the Ba 1- x Pr x Fe 1- y Co y O 3-delta oxides were measured versus temperature in air. The oxygen content increases with increasing iron and praseodymium concentrations in Ba 1- x Pr x Fe 1- y Co y O 3-delta . The value of the thermal expansion coefficient weakly depends on the composition of solid solutions. The conductivity of Ba 1- x Pr x Fe 1- y Co y O 3-delta is practically independent of the concentration of 3 d metals and increases significantly with increasing praseodymium content. The maximum conductivity value of 210 S/cm is obtained for Ba 0.4 Pr 0.6 Fe 0.8 Co 0.2 O 3-delta at 450 degrees C in air. A positive value of the Seebeck coefficient indicates the predominant p - type conductivity in Ba 1- x Pr x Fe 1- y Co y O 3-delta .

The crystal structure, oxygen content and homogeneity range of Pr1-xSrxCoO3-õ solid solutions from room temperature (RT) up to 1100 °C in air were studied. It has been shown that an increase in temperature and Sr content causes an Orthorhombic → Rhombohedral → Cubic transformation of the crystal structure. The heterovalent substitution of Sr2+ for Pr3+ is compensated by an increase in the mean oxidation state of Co ions (zCo) and the formation of oxygen vacancies. The temperature dependences of thermal expansion and conductivity of Pr1-xSrxCoO3-õ solid solutions are explained from the point of view of crystal and defect structure. The diagram of phase relation in the PrCoO3 – “SrCoOz” cross section has been constructed.

La 1.4 Ca 0.6 Ni 0.6 Fe 0.4 O 4+ delta (LCNF), La 1.4 Sr 0.6 Ni 0.6 Fe 0.4 O 4+ delta (LSNF), La 1.4 Ba 0.6 Ni 0.6 Fe 0.4 O 4+ delta (LBNF) have been synthesized by the citrate -nitrate technique. The X -Ray powder diffraction (XRPD) results show an increase in the unit cell parameters and the unit cell volume with the increase in radius of the alkaline earth metal. The oxides possess oxygen excess equal to 0.06 at room temperature and demonstrate semiconductor -type behavior in the 25 - 950 degrees C range. The thermal expansion coefficient (TEC) determined in the 200 - 1000 degrees C interval decreases from 13.9 x 10 -6 (A=Ca) to 13.2 x 10 -6 & Kcy; - 1 (A=Ba) with increasing the dopant size. The electrochemical studies have revealed that the overall polarization resistance of La 1.4 A 0.6 Ni 0.6 Fe 0.4 O 4+ delta is equal to 1.85, 2.61 and 0.4 Omega cm 2 at 800 degrees C for A=Ca, Sr and Ba, respectively. The predominant contribution to the polarization resistance is assigned to the charge transfer - ionic diffusion in the electrodes. It decreases in the row LSNF-LCNFLBNF, which correlates with the increase in ionic conductivity in the oxides.

The magnetic properties of disordered Nd0.5Ba0.5Mn0.5Fe0.5O3-delta/2 and ordered NdBaMnFeO6-delta perovskites were investigated through temperature- and field-dependent DC-magnetization measurements. The temperature dependence of magnetic susceptibilities revealed that antiferromagnetic ordering occurs at temperatures below 185 K for the disordered Nd0.5Ba0.5Mn0.5Fe0.5O3-delta/2 sample, whereas the ordered NdBaMnFeO6-delta perovskite exhibited a paramagnetic state throughout the entire temperature range examined. Notably, the disordered sample exhibited a glassy state, even at room temperature, which transformed into an antiferromagnetic state under higher applied magnetic fields. The magnetic ordering in the disordered Nd0.5Ba0.5Mn0.5Fe0.5O3-delta/2 perovskite and the magnetic-disordering state in the structurally ordered NdBaMnFeO6-delta perovskite could be attributed to the alteration of the oxidation state of Mn.

The homogeneity ranges and crystal structure of solid solutions of Nd _1 - x BaxCo _1 - y FeyO _3 - δ composition were detected. Depending on introduced barium concentration Nd _1 - x BaxCo _1 - y FeyO _3 - δ oxides have been crystallized in the orthorhombically distorted (x = 0.05, sp. gr. Pbnm), cubic (0.6 ≤ x ≤ 0.9, sp. gr. Pm-3m) perovskite structure or double perovskite structure NdBaCo _2 - x FexO _5 + δ (0.0 ≤ x ≤ 1.4, sp. gr. P4/mmm). The dependencies of unit cell parameters versus composition of the Nd _1 - x BaxCo _1 - y FeyO _3 - δ solid solutions were obtained. It is shown that the values of oxygen nonstoichiometry in Nd _1 - x BaxCo _1 - y FeyO _3 - δ , determined by a thermogravimetric method within the temperature range 298–1373 K in air, increased with the raise of barium and cobalt content. Average values of thermal expansion coefficients for the Nd _1 - x BaxCo _1 - y FeyO _3 - δ oxides (0.8 ≤ x ≤ 0.9 and 0.7 ≤ y ≤ 0.9) visibly increased with temperature from (13.5–14.5) × 10–6 K–1 at 300–700 K up to (23.2–26.2) × 10–6 K–1 at 700–1373 K.

Surface oxygen exchange in the La2NiO4+a and La1.5Sr0.5Ni1-yFeyO4+a (y = 0.3, 0.4) oxides is analyzed using the data on oxygen permeability through the membranes with different thicknesses measured under various oxygen partial pressure P(O2) gradients in the 800 -1000 & DEG;C range. The increase in P(O2) gradient induced surface limitations in La2NiO4+a leading to a predominant role of surface exchange in the overall oxygen flux. The origin of surface exchange limitations in La2NiO4+a is ascribed to a relatively fast decrease in oxygen excess and Ni3+ concentration with P(O2) reduction compared to La1.5Sr0.5Ni0.7Fe0.3O4+a and La1.5Sr0.5Ni0.6Fe0.4O4+a, which retained an oxygen excess. Faster surface exchange kinetics for La1.5Sr0.5Ni0.6Fe0.4O4+a in comparison with that for La1.5Sr0.5Ni0.7Fe0.3O4+a is interpreted on the basis of surface microstructure obtained by electron backscatter diffraction (EBSD). It is suggested that the observed changes in size, shape and crystallographic orientation of grains in La1.5Sr0.5Ni0.6Fe0.4O4+a (compared to La1.5Sr0.5Ni0.7Fe0.3O4+a) could result in a higher amount of 3d-metal cations in surface layers of the oxide. & COPY; 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

It is shown that an excess of Dy in A-site (in amount of 0.2 in formula units) allows synthesizing a single-phase perovskite-related oxide with the 123-type structure at 1100 degrees C in air. Cobalt ions completely fill the octahedrally coordinated positions in the structure of 123-type Dy(1.2)Ba(1.8)Fe(1.8)Co(1.2)O8-delta , while iron together with excess Co is in the pyramidal oxygen coordination. The oxygen content at room temperature of 7.86 decreases with temperature. A slight increase in the slope of thermal expansion observed at T > 200 degrees C. The electrical conductivity, carried out mainly by holes, increases non-linearly with temperature, reaching a maximum value 14.8 S center dot cm(-1) at 900 degrees C. Magnetic measurements allow assuming that Fe3+ are in low spin state, all Co2+ ions are in high spin, and Co3+ can be split into several states depending on coordination.

A systematic study of phase equilibria of the Y2O3 - BaO - Fe2O3 system in the vicinity of YBa2Fe3O8+8 reveals that the actual composition of the 123-type oxide differs from the ideal one. It is shown that a single-phase oxide with a 123-type structure can be obtained at 1373 K in air only with a slight deficit of Ba and an excess of both Y and Fe components. The overall formula of the single-phase 123-type oxide is written as Y1.05Ba1.92Fe3.03O8+8. The composition of one more complex oxide, which is absent in the reported earlier phase diagram, is also found to be Ba-deficient; it can be presented as Y1.04Ba0.96FeO4. As a result, the revised version of phase diagram for the Y2O3 - BaO - Fe2O3 system is constructed at 1373 K in air.

Anion-deficient perovskite-like Ba3SmFe2O7.5 was prepared using a glycerol-nitrate synthesis. Using high-temperature X-ray diffraction in situ a crystal structure transition temperature range 800 and 840 ? was established. These results were further confirmed by high-temperature dilatometric analysis. The average thermal expansion coefficient (TEC) of Ba3SmFe2O7.5 is about 12.8 x 10(-6) K-1 between 25 ? and 800 ?. Magnetic experiments proved an excellent phase purity of the oxide and reveal that Fe3+ ions stay in high and intermediate spin states in a ratio of 75% and 25% respectively.

The citric-nitrate technique was used to synthesize polycrystalline Nd2Ni1-xCoxMnO6 & delta; (0.2 & LE; x & LE; 0.5) perovskite oxide. Phase formation was studied by X-ray powder diffraction (XRPD). The unit cell parameters and unit cell volume were refined by the Rietveld analysis, increase with the increasing doping concentration of cobalt. The optical study was performed for the samples in the range of 200-800 nm using UV-vis spectroscopy an absorption peak has been observed in around 330 nm. The energy bandgap (Eg) of the studied samples is slightly influenced by the increasing concentration of cobalt due to the interaction of electronic states between doped Co and other 3d metals. Partial substitution of nickel by cobalt at B-site decreases the Curie temperature (TC) and increased the irreversibility between the zero-field cooled (ZFC) and field-cooled (FC) below TC. The decreasing tendency of TC for the studied samples with the increasing concentration of cobalt in Nd2Ni1-xCoxMnO6 & delta; might be associated with the decreasing Ni/Co-O-Mn bond angle.

A series of samples with the overall composition Gd1-xSrxCo1-yFeyO3-δ (x = 0.8; 0.9 and 0.1 ≤ y ≤ 0.9), which are promising materials for catalytic and SOFC application, was prepared by a glycerol nitrate technique. X-ray diffraction analysis allowed to describe Gd0.2Sr0.8Co1-yFeyO3-δ with 0.1 ≤ y ≤ 0.5 in a tetragonal 2ap × 2ap × 4ap superstructure (SG I4/mmm), while oxides with 0.6 ≤ y ≤ 0.9 exhibit cubic disordered perovskite structure (SG Pm-3m). All Gd0.1Sr0.9Fe1-yCoyO3-δ oxides within the composition range 0.1 ≤ y ≤ 0.9 possess the cubic perovskite structure (SG Pm-3m). The structural parameters were refined using the Rietveld full-profile method. The changes of oxygen content in Gd1-xSrxCo1-yFeyO3-δ versus temperature were determined by thermogravimetric analysis. The introduction of iron into the cobalt sublattice leads to a gradual increase in the unit cell parameters and unit cell volume, accompanied with increasing oxygen content. The temperature dependency of conductivity for Gd0.2Sr0.8Co0.3Fe0.7O3-δ exhibits a maximum (284 S/cm) at ≈600 K in air. The positive value of the Seebeck coefficient indicates predominant p-type conductivity in the Gd0.2Sr0.8Co0.3Fe0.7O3-δ complex oxide.

La2NiO4+delta, La1.4Ca0.6Ni0.6Fe0.4O4+delta (LCNF0604), La1.4Sr0.6Ni0.6Fe0.4O4+delta (LSNF0604), La1.4Sr0.6Ni0.5Fe0.5O4+delta(LSNF0605) and La1.5Sr0.5Ni0.6Fe0.4O4+delta (LSNF0504) were synthesized by the citrate-nitrate technique with the following four annealing steps at 950 degrees C in air (La2NiO4+delta, LCNF0604, LSNF0604) or in atmosphere with the reduced (10(-5) atm) oxygen partial pressure (LSNF0605, LSNF0504). Phase purity of the samples is confirmed by the X-ray powder diffraction (XRPD). Electrochemical impedance spectroscopy studies of the symmetrical cells based on the proton-conducting La28-zW4+zO54+1.5z (z = 0.85, LWO85) electrolyte reveal that the polarization resistance (R-p) decreases in the row LCNF0604>La2NiO4+delta>LSNF0504>LSNF0604>LSNF0605 in the temperature interval of 600-800 degrees C in wet air. The process at low frequencies related to the surface exchange, provides the most significant contribution to the polarization resistance of the studied cells. Higher polarization resistance for the La2NiO4+delta/LWO85 cell can be associated with blocking of protons/protonic species. The minimal Rp value of 1 Omega cm(2) at 800 degrees C in wet air is demonstrated by the LSNF0605/LWO85 symmetrical cell. The maximal power density for the anode-supported LSNF0605/LWO85/Ni-LWO85 single fuel cell is equal to 55 mW cm(-2) at 750 degrees C. The performance of the fuel cell is limited by the formation of La2O3 at the LWO85/Ni-LWO85 interface due to chemical interaction between NiO and LWO85. To improve the performance of the studied fuel cell the development of new proton-conducting buffer layer stable to LWO85 is required.

The phase diagram for the 1/zY(2)O(3)-1/zFe(2)O(3)-CoOx system is experimentally studied and constructed at 1373 K in air. It is also assessed for various temperatures inside 1173-1573 K interval based on the homogeneity ranges of YFe1-xCoxO3 and mixed cobalt/iron oxide phases. The stability boundary of YFe1-xCoxO3 oxides in respect to Po-2 is estimated. It is shown that the limiting composition of YFe1-xCoxO3 solid solution at 1373 K is linearly decreasing from x=0.45 in air down to x=0 corresponding to the decomposition pressure of YFeO3 equal to lg(Po-2/atm)=-13.3.& nbsp;& nbsp;

La2NiO4+δ, La1.4Ca0.6Ni0.6Fe0.4O4+δ (LCNF0604), La1.4Sr0.6Ni0.6Fe0.4O4+δ (LSNF0604), La1.4Sr0.6Ni0.5Fe0.5O4+δ (LSNF0605) and La1.5Sr0.5Ni0.6Fe0.4O4+δ (LSNF0504) were synthesized by the citrate-nitrate technique with the following four annealing steps at 950 °C in air (La2NiO4+δ, LCNF0604, LSNF0604) or in atmosphere with the reduced (10−5 atm) oxygen partial pressure (LSNF0605, LSNF0504). Phase purity of the samples is confirmed by the X-ray powder diffraction (XRPD). Electrochemical impedance spectroscopy studies of the symmetrical cells based on the proton-conducting La28−zW4+zO54+1.5z (z = 0.85, LWO85) electrolyte reveal that the polarization resistance (Rp) decreases in the row LCNF0604>La2NiO4+δ>LSNF0504>LSNF0604>LSNF0605 in the temperature interval of 600–800 °C in wet air. The process at low frequencies related to the surface exchange, provides the most significant contribution to the polarization resistance of the studied cells. Higher polarization resistance for the La2NiO4+δ/LWO85 cell can be associated with blocking of protons/protonic species. The minimal Rp value of 1 Ω cm2 at 800 °C in wet air is demonstrated by the LSNF0605/LWO85 symmetrical cell. The maximal power density for the anode-supported LSNF0605/LWO85/Ni-LWO85 single fuel cell is equal to 55 mW cm−2 at 750 °C. The performance of the fuel cell is limited by the formation of La2O3 at the LWO85/Ni-LWO85 interface due to chemical interaction between NiO and LWO85. To improve the performance of the studied fuel cell the development of new proton-conducting buffer layer stable to LWO85 is required.