CATION DEMIXING IN AN OXYGEN ION CONDUCTOR EXPOSED TO AN OXYGEN POTENTIAL GRADIENT

摘要

This paper gives a formal analysis of cation demixing in an oxygen ion conductor AO_2(+B_2O_3) which is exposed to an oxygen potential gradient and an electronic short-circuit (SOFC conditions). The formal treatment shows that the dopant B becomes enriched at the high oxygen potential side if 3D_B>4D_A, while depletion in B occurs at this side for 3D_B<4D_A. Even small differences in the diffusion coefficients cause appreciable demixing and strongly asymmetric demixing profiles. The paper also discusses the conditions under which demixing might be relevant for applications, e. g. as a long term degradation mechanism.