The di-vacancy diffusion in B2-type Mo-Ta ordered alloy

The formation and diffusion mechanisms of di-vacancies in the ordered Mo-Ta alloy of the B2-type have been investigated by combining the modified analytic embedded-atom method (MAEAM) with molecular dynamic (MD) simulation. From the minimization of the formation energy or the maximization of the binding energy we know that the stability of the di-vacancy configurations decreases in the direction 1 nn Mo-Ta, 2 nn Ta-Ta and 2 nn Mo-Mo, whereas the 4 nn Mo-Ta, 3 nn Ta-Ta and 3 nn Mo-Mo configurations are unstable and tend to congregate to the former three stable configurations (e.g. “2 nn” means “second nearest neighbor” etc.). Taking into account the minimization of the migration or activation energies we also know that, for all six types of the di-vacancy configurations, the multi-jumps involving a series of 1 nn-jumps are energetically more favorable than either one-jump or two-jump diffusion mechanisms. Furthermore, the three stable configurations of the 1 nn Mo-Ta di-vacancy are not only easy to form, but also easy to migrate especially by the four-jump mechanism.