Surface oxygen exchange of La0.3Sr0.7CoO3-delta

The surface oxygen exchange of La0.3Sr0.7CoO3-delta has been studied by O-18/O-16 exchange followed by dynamic SIMS analysis in the temperature region 700-900 degrees C at a p(O2) of 2.1x10(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(O2) of 2.1x10(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(O2)(n) with n=0.41+/-0.02 at 800 degrees 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.