Diffusion correlation effects and the isotope effect in intermetallic compounds

Abstract

There has been considerable discussion in the literature about the various roles and meanings of the diffusion correlation factors in ordered alloys. In this paper diffusion in a two-dimensional stoichiometric ordered alloy model is considered. Using a combination of Monte Carlo simulation and analytical development we consider how the correlation factor for diffusion, as would be found from an isotope effect experiment, is related to the actual correlation factor (all jumps included) and the correlation factor for effective diffusion by the six-jump-cycle mechanism. It is shown that the apparent correlation factor from an isotope effect experiment can deviate very greatly from the actual correlation factor but extrapolates precisely to that for the six jump cycle when the long range order parameter approaches unity. This clarifies the relationships between the various correlation factors in ordered alloys where intersublattice jumps predominate.