Investigation of Diffusion Mechanism in Lanthanum Chromites.

Abstract

Diffusion coefficients of oxide ion and cations in alkaline-earths doped lanthanum chromites were determined by secondary ion mass spectrometry (SIMS). The contribution of grain boundary as a fast diffusion path was quantitatively evaluated by analyzing the depth profiles. The grain boundary diffusion coefficients were 104 times higher than the bulk diffusion coefficients for oxide ion, and 105 times higher for cations. For A-site cation diffusion, the diffusion mechanism at grain boundary has been found to be closely related with the valence state of chromium ion, which will play a main role of determining the vacancy concentration at A-site in the vicinity of grain boundaries. The oxygen partial pressure dependence of oxide ion diffusion coefficient was determined by annealing in Ar-18O2 and Ar-H2-C18O2, and the results revealed a good agreement with the data of oxygen permeation fluxes which were measured in steady state under a large gradient of oxygen partial pressure.