Test of the validity of the Darken/Manning relation for diffusion in ordered alloys taking the L12 structure

In this paper we explore the validity of the Darken/Manning relation between the interdiffusion coefficient and the tracer diffusion coefficients in ordered alloys A(3)B of the Ll(2) type. The analysis centres on Manning's (1968) expression for the vacancy wind factor. The model uses six atom-vacancy exchange frequencies which include intersublattice (alpha <----> beta) and intrasublattice (alpha <----> alpha) jumps for both atomic components. Computer simulation is used to calculate the vacancy wind factor. In general, it is found that the actual vacancy mind factor is usually slightly larger than that predicted by the Manning formalism but overall it is clear that the Manning expression for this factor does very well: the use of Manning's expression for the vacancy wind factor would at worst underestimate the interdiffusion coefficient by about 30-40%.