L. A. Dunyushkina

Electroconductivity and nature of ion transfer in La1 − xSrxSc1 − yMgyO3 − α system (0.01 ≤ x = y ≤ 0.20) in dry and humid air

The conductivity and ion and proton transfer numbers were measured in La1 − xSrxSc1 − yMgyO3 − α system (x = y = 0.10–0.20). The partial conductivities (total ion, proton, oxygen, hole) and their effective activation energies were calculated. The measurements were carried out in air with respect to humidity (pH2O = 0.04−2.65 kPa) within the temperature range from 630 to 920°C.

Proton conductivity and interphase interaction in CsH2PO4-SrZrO3 composites

Microstructure, transport, and thermal properties of the composites of (1 − x)CsH2PO4/xSrZrO3 (x = 0.01–0.2) are studied. Introduction of highly dispersed strontium zirconate results in an increase in low-temperature conductivity by 1–3 orders of magnitude as depedent on the composition, leveling, and disappearance of a superionic phase transition in CsH2PO4. The methods of differential scanning calorimetry and thermogravimetry were used to show that a significant change in thermodynamic properties of CsH2PO4 in composites at x = 0.1–0.2 is observed due to salt amorphization. According to the data of X-ray phase analysis, there is no chemical interaction between the components and no new compounds are formed. An increase in conductivity is caused by salt disordering due to the interphase surface interaction.

Synthesis and properties of CaZrO3 films on YSZ electrolyte surface

CaZrO3 films are studied that were obtained on ceramic supports of solid electrolyte of ZrO2 + 9 mol % Y2O3 (YSZ, yttria stabilized zirconia) from alcohol solutions of zirconium oxychloride and calcium nitrate using the method of dipping with the following drying and annealing. The thickness and morphology of films depend on the concentration of the film-forming solution. Vickers microhardness of the CaZrO3 films was determined. The impedance spectroscopy method was used to study conductivity of films at the temperature of 400–600°C by comparison of impedance spectra of clean supports and supports with a film coating.

Electrode materials for solid oxide fuel cells with proton-conducting electrolyte based on CaZrO3

The work studies chemical stability and thermal compatibility of composite electrodes in contact with proton electrolyte based on calcium zirconate. Composite of electrolytes of CaZr0.95Sc0.05O3–δ and CaZr0.9Y0.1O3–δ with Fe, Ni, Cu, and Pd metals and also with the perovskite oxide of SrTi0.8Fe0.2O3–δ are considered. Temperature dependences of resistance of porous electrodes made of these materials are studied.

Electrical conduction nature and phase transition in CaTi1−xFexO3−δ (x = 0.1–0.5)

Transport numbers for oxygen ions and protons are measured by an emf method in the system CaTi1−xFexO3−δ (x = 0.1–0.5) in the oxidizing and reducing atmospheres in the temperature interval 973–1173 K. It is shown that the compounds under study are mixed ion-electron conductors at small iron concentrations and electron conductors, at large iron contents. The proton conductivity in the compounds is very poor and does not exceed 0.5% in air. On the basis of the temperature dependences of transport numbers for ions and linear expansion, it is established that the CaTi0.9Fe0.1O3−δ system has a phase transition of a second order in a reducing environment at 1020–1050 K. The total and partial electron conductivities of CaTi0.9Fe0.1O3−δ are studied as a function of the partial pressure of oxygen at 1173 K. The nature of electroconduction in CaTi1−xFexO3−δ is discussed.

Electrophysical properties of titanates of alkaline-earth metals

Results on oxygen-ion, electron, and proton conduction and oxygen penetrability of titanates of alkaline-earth metals doped with acceptor admixtures are briefly reviewed. The applicability of these materials in electrochemical devices, in particular, as oxygen-penetrable membranes, is considered. The focus is on the studies carried out at the Institute of High-Temperature Electrochemistry, Ural Branch, Russian Academy of Sciences.

Synthesis, microstructure, and electric properties of CaZr0.9Y0.1O3 – δ films obtained on porous SrTi0.8Fe0.2O3 – δ supports

Compact CaZr0.9Y0.1O3–δ (CZY) film on a porous SrTi0.8Fe0.2O3–δ (STF) support is obtained using the technique of deposition from solutions of inorganic salts in ethanol. According to the data of scanning electron microscopy (SEM), the film has a nanoporous granular structure with the grain size of 0.2 to 1 μm. The thickness of the CZY film on the STF support is about 3 μm after 15-fold solution application. The results of studying the elemental composition showed that elements of the support diffuse into the film in the course of synthesis. Analysis of the data of impedance spectroscopy shows that conductivity of the CZY film is limited the grain bulk. It is assumed that the comparatively low conductivity activation energy of the film (50.3 kJ/mol) is due to diffusion of elements of the STF support that results in variation of the film composition and properties.

Structural and transport properties of compounds in the CsHSO4-KH2PO4 system with a high potassium dihydrophosphate content

The (1−x)CsHSO4-xKH2PO4 system was studied in a wide range of compositions (x = 0.05−0.97). Mixed salts with different crystal structures and different transport, thermodynamic, and thermal properties were shown to form. In these mixed (1−x)CsHSO4-xKH2PO4 compounds (x = 0.05−0.5), solid solutions formed on the basis of the compound with a crystal structure Cs3(HSO4)2(H2PO4) (C2/c). As the content of KH2PO4 increased further, another compound with a crystal structure, CsH5(PO4)2 (P21/c), formed and existed up to x = 0.95. At x ≥ 0.7, KH2PO4 existed as an individual phase along with CsH5(PO4)2; its content increased considerably at x ≥ 0.9. The low conductivities and high activation energies of (1−x)CsHSO4-xKH2PO4 at x = 0.6−0.95 were close to those for CsH5(PO4)2. The compounds with x = 0.5–0.9 showed low thermal stability corresponding to the individual CsH5(PO4)2 phase.

Electrophysical characteristics and stability of solid apatite-like electrolytes La x Si6O12 + 1.5x and La x Ge6O12 + 1.5x

Oxygen-ion conduction in apatite-like compounds based on silicates and germanates of lanthanum LaxA6O12 + 1.5x (A = Si, Ge; x = 9.11–10.22) is studied. The compounds are shown to be purely ionic conductors at 600–900°C and partial oxygen pressures 10−16 to 105 Pa. The electroconductivity of the best conducting specimens of LaxA6O12 + 1.5x (A = Si, Ge; x = 9.77–10) exceeds that of electrolyte YSZ at moderate temperatures. The electroconductivity of lanthanum germanate is substantially greater than that of lanthanum silicate, specifically, 7.85 × 10−2 and 2.35 × 10−2 S cm−1, respectively, at 800°C. An inflection is discovered at ∼750°C in the temperature dependences of electroconductivity of LaxGe6O12 + 1.5x (x = 9.77–10.22). A dilatometric examination points to a second-kind phase transition that may be due to the oxygen sublattice disordering. The behavior of apatite-like electrolytes LaxA6O12 + 1.5x (A = Si, Ge) during long exploitation periods in the interval of working temperatures of electrochemical devices is studied for the first time ever. The electrolytes’ aging at 800°C in air for 1000 h was investigated by the electroconductivity method. The electroconductivity of lanthanum germanates decayed with time by 5% and that of lanthanum silicates, by 9.5%. The steady-state values of electroconductivity of all compounds studied is reached after 600–700 h. The compounds studied form a class of materials that hold some promise as solid electrolytes for medium-temperature fuel cells and other electrochemical devices.

Chemical synthesis and granulometric composition of CaZr 0.9 Y 0.1 O 3–δ powders

CaZr0.9Y0.1O3–δ powders were synthesized by chemical solution methods: modified Pechini method and from solutions of inorganic salts in water and ethanol. The structure crystallizes into the orthorhombic type upon annealing at 1000°C for powders prepared by the Pechini method and from solution of salts in water. It was shown that CaZr0.9Y0.1O3–δ powders synthesized by various methods have different dispersities. The results obtained in a study of the granulometric composition by the sedimentation method and microscopic analysis enable fabrication of dense and mechanically strong electrolyte films and ceramics.