It is well known that homogeneous mixed oxides (A,B)O show kinetic demixing of the cations when exposed at high temperatures to an oxygen potential gradient. This paper shows that when the cation distribution can be described by a random mixing model (the random alloy model) the resulting demixing analysis for the composition profiles can be greatly simplified, and made exact, by making use of the random alloy sum-rule. It is also shown that analyses based on an assumed linearity of the vacancy composition profile will predict incorrect demixing composition profiles for the cations.
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