Kinetics of gas-phase oxygen exchange with La0.6Sr0.4MeO3 − δ (Me = Mn, Co)

Abstract

The method of isotopic exchange was used to study the kinetics of interaction between the gasphase oxygen and oxides, La0.6Sr0.4MnO3 − δ (LSM) and La0.6Sr0.4CoO3 − δ (LSC), in the temperature range of 600–850°C at the oxygen pressures of 0.13–8.53 kPa. The values of the interphase exchange rate and oxygen diffusion coefficient were determined. Effective activation energies of the oxygen exchange and diffusion processes were 0.71 ± 0.16 and 1.42 ± 0.32 eV for LSM and 0.11 ± 0.03 and 1.08 ± 0.19 eV for LSC, accordingly. The contributions of the three oxygen exchange types were calculated. It was found that the exponent in the dependence of the interphase exchange rate on \(P_{O_2 }\) (n) and the exponent in the dependence of the concentration of oxygen vacancies in the oxide on \(P_{O_2 }\) (ɛ) are related as: n = 1 + ɛ. Fulfillment of this relationship implies participation of the molecular form of oxygen (O2)a on the surface of the studied oxides as the rate-determining stage of exchange.