Oxygen tracer diffusion and surface exchange kinetics in La0.6Sr0.4CoO3-δ

The oxygen tracer diffusion coefficient, D*, and the oxygen tracer surface exchange coefficient, k*, were measured in La0.6Sr0.4CoO3-delta over the temperature range of 406-680 degrees C and the oxygen partial pressure range 0.044-1.019 bar. Distortions of the near surface regions of the diffusion profiles were observed in several specimens. O-18 exchange experiments were modeled by the Finite Element method and the origin of the observed distortions was assigned to exchange of oxygen during sample cooling. The estimated error in the determination of D* and k* was found to be less than 20%. The activation energies of D* and k* were 1.84 +/- 0.02 eV and 0.76 +/- 0.13 eV, respectively. D* was found to decrease with oxygen partial pressure following the power law with a power of -0.55 +/- 0.10. The effect of Sr doping on the values of D* in Ln(1-x)Sr(x)CoO(3-delta) (Ln = La, Sm) perovskites is discussed. The data obtained from isotopic exchange measurements at 500-600 degrees C are in good agreement with the kinetic parameters derived from conductivity relaxation experiments on samples from the same batch. (C) 2010 Elsevier B.V. All rights reserved.