In this review article, the authors first introduce the phenomenological transport coefficients, and the relationships between them and the tracer diffusion coefficients. Next, the authors discuss a sum rule relating phenomenological coefficients themselves in the random-alloy model. The authors then consider several applications of the sum rule to diffusion problems. These applications include intrinsic diffusion in multicomponent alloys, chemical diffusion in strongly ionic mixed cation crystals, and the segregation (demixing) of cations in mixed oxides in an oxygen potential gradient and/or an electric field. In each case, a substantial simplification is possible as a result of the sum rule.
Journal of Phase Equilibria and Diffusion Vol. 26, no. 5, p. 503-509