Oxygen�@Permeation Chromites Mechanism in Lanthanum, La_l-xCa_xCr0_3-delta

@ The oxygen permeation mechanism through La_1-xCa_xCr0_3-delta was investigated by two experimental methods, firstly by the determination of the oxygen tracer diffusion coefficient by ¹⁸O₂ exchange in different oxygen partial pressures and SIMS analyses, and secondly by the direct measurement of the permeation flux in a steady state under a p(02) gradient. The oxygen tracer diffusion coefficient increased with decreasing oxygen partial pressure in the range p(0₂) = 10^-9 to I Pa at T = 1 273 K. On the contrary, the oxygen vacancy diffusion coefficient was found to be I .7 x 10^-9 m² s^-1 which was independent of oxygen partial pressure or oxygen vacancy content. The oxygen permeation flux as oxide ion current density (J₀^2-) through La_l-xCa_xCr0_3-delta was determined by using an electrochemical method in the p(0₂) range from 10^-11 to 10⁵ Pa at T = 1273 K. When p(0₂) was lower than l0^-5 Pa, J0^2- was suppressed by the effect of surface reaction as the rate determining step. The contribution of grain boundary diffusion on the permeation flux was considered when p(0²) was larger than I Pa.