Monte Carlo simulation of diffusion in B2 ordered phase

Atomic migration in an ordered binary alloy with B2 structure is studied by atomistic Monte Carlo simulations where atom migration results from exchanges with a single vacancy on a rigid lattice. Highly correlated vacancy sequences are observed and studied using improved residence time algorithms. Beside the classical 6-jump cycle a wide range of other correlated sequences is also identified. Furthermore, when interaction energies of the model present a high degree of asymmetry, two effects have been observed: tracer diffusion coefficient ratio can be as large as 4.5 which can be rationalized in terms of the identified sequences; diffusion coefficients exhibit an upward curvature below the order-disorder transition temperature. These two effects have been observed in some alloys such as CoGa and therefore can be qualitatively reproduced without the need to invoke a divacancy mechanism.