Solid-state coulometric titration was used to determine the O non-stoichiometry of La0.5Sr0.5FeO3-x at 800 to 1000C and 10−16 ≤ PO2 ≤ 0.5atm. Above 900C, reproducible data were obtained on both increasing and decreasing PO2. At up to 850C, a discontinuity appeared in the variation of the O non-stoichiometry with PO2 indicative of 2-phase behavior. The electrical conductivity of La0.5Sr0.5FeO3-x was determined at 800 and 900C and 10−14 ≤ PO2 ≤ 0.3atm by using a 4-probe ac technique. Slow equilibration kinetics were observed in the intermediate PO2 region (about 10−5atm) due to either short-range order of O vacancies or phase separation between a perovskite phase and a vacancy ordered phase. The isotherms were reproducible, irrespective of the direction of the PO2 change, provided that sufficiently long equilibration times were used.

Determination of the Equilibrium Oxygen Non-Stoichiometry and the Electrical Conductivity of La0.5Sr0.5FeO3-x. J.Yoo, C.Y.Park, A.J.Jacobson: Solid State Ionics, 2004, 175[1-4], 55-8