Computer simulation was used to investigate the validity of the Darken-Manning relationship between the chemical diffusion coefficient and the tracer diffusion coefficients of the components, in these stoichiometric intermetallic compounds, for vanishingly low vacancy contents. The analysis concentrated upon the validity of Manning’s random-alloy expression for the vacancy-wind factor. The models for the D03 and A15 structures used 8 atom-vacancy exchange frequencies. In the case of the D03 structure, it was found that the actual vacancy-wind factor was usually slightly larger than that predicted by Manning, but the overall agreement was good. The use of Manning’s expression was expected to underestimate this factor by some 30 to 40% at worst. A similar result was found in the case of the A15 structure; except when diffusion along the chains of the structure was rapid. Manning’s expression failed badly when a constant geometrical tracer correlation factor was used. In the case of both structures, if the geometrical correlation factor was varied so as to reflect the structure which was actually explored by the atoms (mainly those in the majority), the agreement was markedly improved.

Relating Tracer and Chemical Diffusion Coefficients in Intermetallic Compounds taking the D03 and A15 Structures. I.V.Belova, G.E.Murch: Journal of the Physics and Chemistry of Solids, 1999, 60[12], 2023-9