Determination of the equilibrium oxygen non-stoichiometry and the electrical conductivity of La0.5Sr0.5FeO3-x

Solid-state coulometric titration has been used to determine the oxygen non-stoichiometry of La0.5Sr0.5FeO3-x at 800≤T≤1000 °C and 10−16≤pO2≤0.5 atm. Above 900 °C, reproducible data were obtained on both increasing and decreasing pO2. At temperatures T≤850 °C, a discontinuity appears in the variation of the oxygen non-stoichiometry with pO2 indicative of two-phase behavior. ectrical conductivity of La0.5Sr0.5FeO3-x was determined at 800 and 900 °C and 10−14≤pO2≤0.3 atm by a FOUR-probe ac technique. Slow equilibration kinetics were observed in the intermediate pO2 region (∼10−5 atm) due to either short-range order of oxygen vacancies or phase separation between a perovskite phase and a vacancy ordered phase. The isotherms are reproducible, irrespective of the direction of the pO2 change, provided long enough equilibration times are used. The criteria for equilibrium used in the experiments are discussed.