A theory of tracer diffusion in non-stoichiometric intermetallic compounds

In this paper, the six-jump-cycle mechanism, which was conceived as a minimum-energy-penalty sequence of jumps for certain stoichiometric alloys showing antistructural disorder, is extended to non-stoichiometric compositions for alloys taking the B2 structure. We make use of the five-frequency model for impurity diffusion as a convenient framework for expressing our formalism; the antistructural atoms are analogous to the 'impurity' and the six-jump cycle acts as the diffusion mechanism unit. We derive expressions for the tracer diffusivity for both atomic components by utilizing the Ising alloy model. Monte Carlo simulation is used to test the expressions obtained; there is very good agreement.