DIFFUSION AND SURFACE EXCHANGE COEFFICIENTS IN MIXED IONIC ELECTRONICCONDUCTING OXIDES FROM THE PRESSURE-DEPENDENCE OF OXYGEN PERMEATION

Using a simple model for the dependence of the net surface oxygen exch ange flux on the chemical potential drop at the gas-MIEC interface, we are able to deduce the ambipolar diffusion coefficient D-a, and the s urface exchange rate coefficient ki, from the dependence of oxygen per meation on the oxygen pressure gradient. From permeation measurements on tubular membranes we report for SrCo0.8Fe0.2O3-delta at 890 degrees C the values D-a = 8.3 X 10(-6) cm(2)s(-1) and k(10) = 2.1 X 10(-4) c m s(-1) and for Sm0.5Sr0.5CoO3-delta at 915 degrees C the values 8.6 X 10(-7) cm(2)s(-1) and 6 X 10(-5) cms(-1).