Effect of oxygen nonstoichiometry on kinetics of oxygen exchange and diffusion in lanthanum-strontium cobaltites

Abstract

The method of isotopic exchange was used to study the kinetics of oxygen exchange and diffusion in complex oxides of La1 − x Sr x Co1 − y Fe y O3 − δ (x = 0.0, y = 0.0; x = 0.6, y = 0.2, 0.4). The rates of oxygen interfacial exchange and its diffusion coefficient were determined for LaCoO3 − δ at the pressure of 5 torr in the temperature range of 600–850°C and at the temperature of 700°C in the pressure range of 1–70 torr. The contributions of the three exchange types were calculated. The order of the dependence of the interfacial exchange rate on the oxygen pressure was 0.51 ± 0.01. In the case of La0.4Sr0.6Co1 − y Fe y O3 − δ (y = 0.2, 0.4) in the temperature range of 600–900°C at the oxygen pressure of 10 torr, the oxygen exchange rates and diffusion coefficients were determined in the material bulk and in the subsurface region; contributions of the three types of exchange were calculated. The paper considers the mechanism of oxygen exchange and diffusion as compared to nonstoichiometry in the oxygen sublattice of the La1 − x Sr x Co1 − y Fe y O3 − δ oxides.