Atomic transport in ionic solid solutions

Summary This paper examines certain aspects of the relation of tracer diffusion coefficients to the corresponding so-called intrinsic diffusion coefficients arising in chemical interdiffusion in binary solid solutions. Although no exact general relation between these quantities is to be expected, the existence of such a relation for the solute species is to be anticipated in dilute solid solutions. In metallic alloys they become equal in the dilute limit, but in solid solutions of ionic conductors the ratio depends on details of the system (in particular on the solute and solvent ion charges and the degree of association between solute ions and charge compensating defects). Both the macroscopic and microscopic theories of these ionic solutions are described. A rather clear conflict exists between the theoretical predictions and some existing experimental results on the system Cr₂O₃ in MgO. In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching.