Oxygen nonstoichiometry and defect equilibria in La0.49Sr0.5–xBaxFeO3–δ

Abstract

High level of mixed-conductivity and good stability of oxide La0.5Sr0.5FeO3–δ make it promising for the development of functional materials for such energy-related applications as solid oxide fuel cells and membrane reactors for partial oxidation of methane. The oxygen content in La0.49Sr0.5−xBaxFeO3–δ (x = 0, 0.25, 0.5) was measured by means of coulometric titration in the interval of partial oxygen pressure between 10−20 and 0.5 atm at temperatures 750–950 °C. The obtained results were employed for defect structure analysis of oxides. An ideal solution model enabled satisfactory simulation of experimental data for barium-free oxide. A reasonable data description for barium-containing oxides was achieved in the model, assuming that some of the oxygen vacancies are unavailable for oxygen ions. Partial substitution of barium for strontium was found to decrease the oxidation reaction constant of iron ions, resulting in a raised concentration of n-type electronic charge carriers and a reduced concentration of p-type carriers.