Test of the validity of the Darken/Manning relation for diffusion in ordered alloys taking the L1(2) structure

In this paper we explore the validity of the Darken/Manning relation betwee n the interdiffusion coefficient and the tracer diffusion coefficients in o rdered alloys A(3)B of the Ll(2) type. The analysis centres on Manning's (1 968) expression for the vacancy wind factor. The model uses six atom-vacanc y exchange frequencies which include intersublattice (alpha <----> beta) an d intrasublattice (alpha <----> alpha) jumps for both atomic components. Co mputer 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 in terdiffusion coefficient by about 30-40%.