A new interpretation of tracer diffusion in Co-Ga

Abstract

Abstract Tracer diffusion of Co and Ga in Co–Ga has formerly been described primarily in terms of a triple-defect mechanism based on a divacancy mechanism and the existence of triple-defect disorder. Using the interaction energies employed to describe the partitioning of the vacancies and atoms in Co–Ga by Waegemaekers and Van Ommen (1982, J. Phys. F, 12, 2829) we have performed Monte Carlo simulations of the tracer diffusivities in Co–Ga. We make use of a general isolated vacancy diffusion model with nearestneighbour jumps with no explicit or implicit binding between the vacancies that others have suggested previously. The model is fully consistent with triple-defect disorder in Co–Ga. We show that the tracer diffusion data can be well described in Co–Ga without the need for the triple-defect mechanism. It is found that Ga makes the equivalent of a next-nearest-neighbour jump by jumping via the Co sublattice where it has a very short residence time whereas the triple-defect mechanism requires a formal next-nearest-neighbour jump for Ga. It is commented that tracer diffusion measurements alone probably cannot resolve this difference.