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The surface oxygen exchange of Lao.3Sro,, Co0,_6 has been studied by 'SO/'hO exchange followed by dynamic SIMS analysis in the temperature region 700-900°C at a po, of 2.1 X lo4 Pa. The activation energy for the surface exchange rate (k) is 283 kJ mol -' and for the oxygen tracer diffusion coefficient (D *) 56t4 kJ mol-' The absolute values for both k and D * are among the highest known in the literature. The characteristic thickness at a po, of 2.1 X lo4 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& with n =0.41 to.02 at WYC, 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.

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