N. A. Tarasova

Electric properties of oxyfluorides Ba2In2O5−0.5xFx with brownmillerite structure

Synthesis of fluoro-substituted substances based on brownmillerite Ba2In2O5 is carried out. The width of the homogeneity region of the Ba2In2O5−0.5xFx (0 < x ≤ 0.25) solid solution was established using X-ray analysis. Measurement of temperature dependences of conductivity in atmospheres with different partial pressure of water vapor (pH2O = 3.3 and 2 × 103 Pa) showed an increase in conductivity at T ≤ 550°C in a humid atmosphere, which is due to appearance of proton transport. The dependence of conductivity on partial oxygen pressure (pO2 = 0.21 × 105 to 10−15 Pa) is studied in the temperature range of 500–1000°C; ion transport numbers are calculated. The method of polarization measurements was used to determine transport numbers of fluoride. Total conductivity is divided into ion (proton, oxygen, and fluoride ion) and electron components. Analysis of concentration dependences of conductivities showed that low concentrations of fluoride allow increasing both the total and partial conductivities (oxygen-ion and proton) and, besides, allow shifting the “order-disorder” phase transition by 100°C to the low temperature range.

Effect of anion doping on mobility of ionic charge carriers in solid solutions based on Ba2In2O5

In the work, mobilities of oxygen and protons are determined for F−-substituted solid solutions based on brownmillerite Ba2In2O5 and their concentration dependences are analyzed. It is found that small additives of the more mobile anion (F− ions) promote an increase in oxygen mobility as a result of additional effects of repulsion of ions of different nature in the anion sublattice. Mobility of oxygen at high fluoride concentrations decreases due to the overlapping of migration paths of diffusion, as both anions, fluoride ions and oxygen ions, move via oxygen vacancies. Concentration dependences of mobility of proton carriers have a similar character, which is related to the effect of the oxygen sublattice. The anion doping method used in the work can be recommended as the general method for improvement of the transport characteristics of oxygen-ionic and protonic conductors with a perovskite-like structure.

Hydration and forms of oxygen-hydrogen groups in Oxyfluorides Ba2 − 0.5xIn2O5 − xFx

A number of fluorine-substituted compounds were synthesized from brownmillerite Ba2In2O5. The homogeneity range of the Ba2 − 0.5xIn2O5 − xFx solid solution (x ≤ 0.3) was determined by X-ray diffractometry. The studied phases were found to be able to incorporate water from the gas phase, due to which their orthorhombic structure transforms into tetragonal one. The degree of hydration decreased as the fluorine content in the solid solution increased. As in the case of Ba2In2O5, the energetically nonequivalent hydroxo groups were found to be the main form of oxygen-hydrogen groups.

Synthesis, hydration, and electrical properties of oxyfluoride Ba2InO3F

Oxyfluoride with a Ruddlesden-Popper structure Ba2InO3F was synthesized. Its monophase character was confirmed and lattice parameters were determined by X-ray diffraction. This oxyfluoride was proven to be capable of hydration and proton conductivity.

Effect of F – -doping on the transport properties of perovskite-like complex oxides

The structural and electric characteristics of fluorine-substituted complex oxides obtained by anion doping based on Ba2CaNbO5.5 and Ba2In2O5 matrices were compared. The mobility of ion charge carriers was found to depend on the concentration of the dopant anion and oxygen vacancies and the degree of disordering of the latter.

Synthesis, hydration, and electric properties of chlorine-substituted brownmillerite Ba1.95In2O4.9Cl0.1

Chlorine-substituted brownmillerite Ba1.95In2O4.9Cl0.1 was obtained from barium indate Ba2In2O5 by solid-phase synthesis. The ability to absorb water from the gas phase was confirmed by thermogravimetric studies. The transport properties were studied while varying the thermodynamic parameters of the external environment (T, pO2, pH2O). The chloride ions in the oxygen sublattice of barium indate Ba2In2O5 were found to affect the ion conductivity. In a humid atmosphere, the sample exhibited proton conductivity (Ea = 0.54 eV), whose contribution became dominant below 300°C.