ATOMIC TRANSPORT IN IONIC SOLID-SOLUTIONS

This paper examines certain aspects of the relation of tracer diffusio n coefficients to the corresponding so-called intrinsic diffusion coef ficients 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 t o be anticipated in dilute solid solutions. In metallic alloys they be come equal in the dilute limit, but in solid solutions of ionic conduc tors the ratio depends on details of the system (in particular on the solute and solvent ion charges and the degree of association between s olute 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 exi sting experimental results on the system Cr2O3 in MgO.