Atomic migration in ordered binary alloys with B2 structure was studied by atomistic Monte Carlo simulations where atom migration results from exchanges with a single vacancy on a rigid lattice. Highly correlated vacancy sequences were observed and studied using improved residence time algorithms. It was shown that, for partially ordered structures, the classical six-jump cycles contribute only partially to the diffusion process, and that a wide range of other correlated sequences were observed, including a proposed antisite bridge mechanism. Among the other sequences, six-jump cycles were identified that were assisted by antisites. Furthermore, when atomic interaction energies presented a high degree of asymmetry, two effects were observed: the ratio of tracer diffusion coefficients increased as a result of additional loops involved in the six-jump cycles; diffusion coefficients exhibited an upward curvature below the order-disorder transition temperature. These two effects were observed in some alloys 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. See also: Defect and Diffusion Forum, 1997, 143-147, 297-302