Atomic migration in ordered binary alloys with the B2 structure, where atom migration resulted from exchanges with a single vacancy on a rigid lattice, was studied by means of atomistic Monte Carlo simulations. Highly correlated vacancy sequences were observed, and were studied by using improved residence-time algorithms. It was shown that, for partially ordered structures, classical 6-jump cycles contributed only partially to the diffusion process, and that a wide range of other correlated sequences was observed; including a recently proposed antisite bridge mechanism. Among other sequences, 6-jump cycles that were assisted by antisites were identified. When the atomic interaction energies exhibited a high degree of asymmetry, 2 effects were observed. That is, the ratio of tracer diffusion coefficients increased as a result of additional loops which were involved in the 6-jump cycles. The diffusion coefficients exhibited an upward curvature below the order/disorder transition temperature. These effects were observed in alloys such as Co-Ga and could therefore be qualitatively reproduced, without invoking triple defects.

Identification of Novel Diffusion Cycles in B2-Ordered Phases by Monte Carlo Simulation M.Athènes, P.Bellon, G.Martin: Philosophical Magazine A, 1997, 76[3], 565-85