Chemical interdiffusion via Schottky vacancy-pairs in strongly ionic crystals was analysed for diffusion couples (AY-BY), where A and B had the same valence. A sum-rule was derived which related the phenomenological coefficients. This was based upon an earlier sum-rule for diffusion in a multi-component random alloy, via isolated vacancies. With this sum-rule, and other relationships, it was shown that the ratio of the intrinsic diffusivities could be expressed in exactly the same simple form as for diffusion via isolated vacancies. The functional form for the interdiffusion coefficient, when expressed in terms of atom-vacancy exchange frequencies for diffusion, was found to be essentially the same as that for isolated vacancies. The difference involved only the relative differences in the local jump coordination of the vacancies in each case.

Analysis of Interdiffusion via Vacancy-Pairs in Strongly Ionic Solids. I.V.Belova, G.E.Murch: Philosophical Magazine, 2004, 84[34], 3637-53