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A quantitative model for the dc voltage‐induced resistance degradation is based on the defect structural material constants and a numerical solution of the general transport problem for the mixed‐conducting perovskite‐type titanates. During degradation, a demixing of the initially homogeneous oxygen vacancy concentration in nominally undoped and acceptor‐doped systems occurs since the ionic transfer is (at least partially) blocked at the electrodes. Because of the specific defect structure, the concentration polarization of the oxygen vacancies leads to a pronounced increase of the p ‐conductivity in the anodic region and formation of an n ‐conducting cathodic region. The results of our phenomenological degradation studies concerning the influence of external parameters and material parameters as well as the time evolution of the field distribution and the electro‐coloration are described by our simulation model with reasonable precision. The thermodynamic and kinetic aspects of the demixing process are discussed and compared to related phenomena.
Baiatu et al. (1990) studied this question.