Surface oxygen exchange of La 0.3Sr 0.7CoO 3 − δ

Abstract

The surface oxygen exchange of La 0.3Sr 0.7CoO 3 − δ has been studied by 18O 16O exchange followed by dynamic SIMS analysis in the temperature region 700–;900 °C at a p O 2 of 2.1 × 10 4 Pa. The activation energy for the surface exchange rate ( k) is 28 ± 5 kJ mol −1 and for the oxygen tracer diffusion coefficient (D∗) 56 ± 4 kJ mol −1 . The absolute values for both k and D∗ are among the highest known in the literature. The characteristic thickness at a p O 2 of 2.1 × 10 4 Pa is calculated to lie in the range 0.70 to 1.3 mm and is a function of temperature. The latter reflects the different activation energies for k and D∗. The surface oxygen exchange coefficient is proportional to P O 2 n with n = 0.41 ± 0.02 at 800 °C, which has been explained by a rate determining step involving an adsorbed oxygen species and an oxygen vacancy. No oxygen pressure dependence for the tracer diffusion coefficient was observed at this temperature.