COMPUTER-SIMULATION OF TRACER DIFFUSION IN A BINARY ORDERED ALLOY WITH AN EQUILIBRIUM CONCENTRATION OF VACANCIES

A procedure is described in which tracer diffusion can be simulated in an (Ising) binary ordered alloy where an equilibrium concentration of vacancies is established and maintained. It was found that equilibrium vacancy concentrations were very high for typical values of the interaction energies. However, in these exploratory calculations, no allowance is made for lattice relaxation about the vacancy and electronic effects asssociated with vacancy formation and such high vacancy concentrations should not necessarily be expected in real systems. The behaviour of the tracer diffusion coefficient, as assembled from its correlated and uncorrelated parts appropriate to the hopping model, is dictated largely by the variation in the exchange frequency and the vacancy concentration, apart from the ordered region where the strong 'physical correlation effect' has to be accounted for.