The Ba3InGa2O7.5 complex oxide, possessing the perovskite-related structure with structural oxygen vacancies, was first synthesized by the solid state method. The phase was found to be characterized by monoclinic symmetry (sp. gr. P2/c) with the following unit cell parameters: a = 7.942(1) Å, b = 5.868(5) Å, c = 18.201(6) Å, b = 91.52(9). Comprehensive investigations of electrical properties were carried out; ceramic material based on the complex oxide was shown to be a predominantly ionic conductor in the temperature range 450–900 oC. The conductivity is due to oxygen-ion transfer in dry conditions and oxygen-ion and proton transfer in wet atmosphere. The proton conductivity value is 4.5·10–5 S/cm, and the proton transport number is ~50% at 700 oC in wet air; at lower temperatures, proton transport becomes dominant. Prolonged treatment of the sample in water vapors below 450 oC leads to hydrolysis decomposition.

The structural and morphological properties of samples in the Ba2In2O5–Ba2InNbO6 eutectic system were studied when treated below and above the eutectic temperature. A narrow-extent Ba2In2-xNbxO5+x (х ≤ 0.05) solid solution and (1 − y)Ba2In1.95Nb0.05O5.05∙yBa2InNbO6 composites were found in the system. In the y ≥ 0.15 composites, the major phase is a stabilized structure with a disordered arrangement of oxygen vacancies. The total electrical conductivity in dry air is determined primarily by oxygen-ion transfer, and it increases for both the solid solution and the composites; the greatest increase of about two orders of magnitude is in the y = 0.15 and 0.25 composite samples treated at above-eutectic temperature. The increase in electrical conductivity is due to the combined influence of structural and morphological factors. The composites treated at above-eutectic temperature have a specific morphology. A layer of submicron-sized crystallites is formed on the surface of the grains of the major phase upon eutectic crystallization, which is responsible for the appearance of the composite electrical conductivity effect.

Properties of the (1-x)Ba2In1.57Al0.43O5 center dot xBa(2)InAlO(5) composite sample (x=0.12) were studied. The composite was found to demonstrate a reversible water uptake at temperatures below 800(degrees)C in wet atmosphere; it leads to proton defects formation in the structures of the phases included the composite. The hydration process is accompanied by a significant increase in the total electrical conductivity due to the appearance of a proton transfer contribution. The sample is predominantly a proton conductor at temperatures below 500 C-degrees in wet air. When the composite ceramics treated above the eutectic temperature of the Ba2In1.57Al0.43O5 - Ba2InAlO5 system, the total electrical conductivity increases compared to the conductivity of the initial phases; composite effect is related to formation of a special microstructure of the sample.

The La2Mo2O9-La2Mo3O12 composite materials represent a novel class of highly conductive materials demonstrating increased oxygen-ion conductivity. Extensive research of (100 - x)La2Mo2O9-xLa2Mo3O12 composites over a wide range of concentrations (x = 5, 10, 15, 20, 30, and 100) was carried out for the first time. An increase in conductivity, oxygen surface exchange coefficient, and oxygen diffusivity is observed for composites compared to individual oxides, which is associated with the segregation of different ions on the surface of the grains and the formation of a La5Mo3O16 new phase at the contact boundary of La2Mo2O9 and La2Mo3O12. 3D-modeling of the composite microstructure was performed on the basis of SEM-image analysis data in order to estimate the conductivity of the interphase layer between the La2Mo2O9 and La2Mo3O12 grains containing La5Mo3O16. The electrical conductivity values of the composite materials calculated from a 3D-simulated microstructure and the experimentally measured conductivity correlate and demonstrate a composite effect.

The complex oxide Ba2InAlO5 was obtained by the solid-phase method. Its thermal and transport properties were studied for the first time while varying the temperature and composition of the gas phase (partial pressure of water and oxygen vapors). The possibility of dissociative incorporation of water in the structure of the complex oxide, leading to the formation of proton defects and proton transfer in the medium temperature range (500–700°C), was established. The conductivity was differentiated into components. It was proved that the total electric conductivity of the phase in dried air is mainly of hole type with a small contribution of oxygen-ion transport. In a humid atmosphere, the contribution and magnitude of ion conductivity increase due to the appearance of proton transfer.

A heterogeneous doping method was used for the first time to modify the transport properties of the oxygen-ion conductor La(2)Mo(2)O(9). The effect of temperature and oxygen partial pressure in the gas phase on conductivity of the obtained composite {0.85La2Mo2O9–0.15La2Mo3O12} was studied. Introduction of 15 mol. % an inert low-conductive additional phase La(2)Mo(3)O(12) results in an increase in conductivity of the matrix phase by nearly 1 orders of magnitude. It is associated with appearance of a composite effect. However, there is no suppression of the α-La(2)Mo(2)O(9)↔β-La(2) Mo(2)O(9) phase transition. It is shown that the conductivity type of both lanthanum dimolybdate and composite based on it is predominantly ionic in the wide range of oxygen partial pressures

Сложнооксидные фазы La2Mo2O9 и La2Mo3O12 получены твердофазным методом. Композит состава 0.9La2Mo2O9 0.1La2Mo3O12 получен механическим смешением компонентов. Контроль фазового состава продуктов осуществлен методом рентгенофазового анализа. Исследованы транспортные свойства, термодинамическая стабильность матричного и композиционного составов. Установлено, что введение инертного гетерогенного допанта La2Mo3O12 способствует увеличению проводимости композита в 610 раз относительно матричного состава, снижению энергии активации электропроводности и повышению стабильности керамики при низких парциальных давлениях кислорода. Однако при этом не происходит подавления структурного фазового перехода La2Mo2O9La2Mo2O9. Эффект роста электропроводности композиционного состава может быть обусловлен частичной стабилизацией в области низких температур высокосимметричной модификации La2Mo2O9. Рассчитанные энергии активации проводимости Ea для La2Mo2O9 равны 0.62 и 1.18 эВ, соответственно, в высоко и в низкотемпературной области. Для композиционного состава значения Ea равны 0.53 и 1.12 эВ, соответственно. La2Mo2O9 является ионным проводником в широком диапазоне парциальных давлений кислорода 10180.21 атм, у композиционного состава вклад электронной проводимости отсутствует вплоть до 1020 атм.

The composites based on the oxygen-ion and proton conductor Ba2In1.7W0.3O5.45 with a 30 mol % Ba2InNbO6 addition were studied. The processing of the compact samples of the composite electrolyte at 1430°C gave ceramics with a density of 95%. The total electric conductivity of the composite in dry and humid atmospheres decreases by ~0.5 order of magnitude compared with the conductivity of the matrix.

Double perovskite Sr2Ni0.75Mg0.25MoO6-δ powders were synthesized by the combustion method using systems containing nitrates and varying amounts of the following organic components: glycine, glycerol, and polyvinyl alcohol. The characteristics (temperature, gas composition, etc.) of the synthesis process were studied and the optimal conditions for obtaining single-phase samples were determined. It was established that the usage of one-and-a-half excess of glycerol as organic component provides the formation single-phase complex oxide. The crystal structure of the obtained complex oxide, which is of interest as an anode material for solid oxide fuel cells, was refined and its physico-chemical properties (specific surface area, particle size, electrical conductivity, and catalytic activity in the reaction of methane oxidation) were investigated.

The effect inert additions of complex oxide Ba2InNbO6 have on the structure and properties of solid electrolyte Ba2In2O5 is studied. It is shown that composite samples of (1 − x) Ba2In2O5 · xBa2InNbO6 acquire improved electrical properties, due to the stabilization of a highly conductive modification of barium indate characterized by a disordered arrangement of oxygen vacancies.

The reasons for the appearance of proton conductivity in the complex oxide Ba2InMO6 phases (M = Nb, Ta) with a formally complete oxygen sublattice were determined. The formation of oxygen vacancies in the structure as a result of the violation of stoichiometry causes the introduction of water, the amount of which does not exceed 0.02 mol per formula unit of the composition. The appearance of proton defects even in low concentrations provides the dominant proton transfer below 500°C.

The paper reports novel proton-conducting composites in the Ba2In2O5–Ba2InTaO6 eutectic oxide system. The samples were prepared in situ by solid state reaction method; their microstructural, thermal and electrical properties were investigated. The results show an essential conductivity enhancement of the (1-x)Ba2In2O5 ∙ xBa2InTaO6 samples both in dry and wet conditions compared with those for Ba2In2O5 and Ba2InTaO6 phases. The effect is maximal (near 2 orders of magnitude) for the composites with x = 0.2, 0.3, which retain a possibility to a water uptake and demonstrate the predominantly proton conduction at temperatures below 500 °C in wet air.