Theory of diffusion in the ordered alloy .1. Tracer correlation effects

In this study, two and four frequency versions of a model of a long range ordered alloy where the sublattices exist a priori are proposed. This model is a natural extension to the ordered state of the well-known random alloy model. Manning's (1971) formalism for describing tracer correlation effects in the random alloy is adapted and extended to the present model. The model is applicable to any lattice which can be conceived as a combination of two sublattices with the same number of sites and where diffusion requires a vacancy jump from one sublattice to the other. Computer simulation results for the simple cubic lattice from a previous study (Belova, Ivory and Murch 1995) and new ones presented here are used to assess the new analysis. The general trends of the correlation factors across the complete frequency range are described very well. The detailed fit is generally better for the faster moving atomic component.