Tracer diffusion in nonstoichiometric intermetallic compounds with random mixing on each sublattice

Tracer diffusion by way of vacancies is investigated in B2 intermetallics AB by means of a kinetic equation approach. The model used is one with four intersub-lattice frequencies where each sub-lattice is treated as a random alloy. Coupling is achieved between the two types of cycles, i.e., with the vacancy starting on one sub- lattice and finishing on either sub-lattice and with a vacancy starting on the other sub-lattice and finishing on either sub-lattice. An expression for the tracer correlation factor is derived in terms of atom vacancy exchange frequencies and atomic concentrations. Results from this expression are compared with Monte Carlo calculations and also results from a previous Manning-type random alloy approach to the problem.