A note on the phenomenological coefficients for atom transport in a dilute random alloy

Abstract

Manning's expressions for the phenomenological atomic transport coefficients for a random alloy are known from computer simulations to be remarkably accurate for concentrated alloys. These expressions for a binary alloy have been evaluated in the dilute solution limit (i.e. correct to first order in the solute concentration) and compared with exact and accurate numerical results for this limit obtained by specializing known results for vacancy models to the random alloy case. It is found that three of the four independent coefficients are given exactly by Manning's expressions. Although there are no exact results for the fourth coefficient (i.e. for the “enhancement factor” for diffusion of tracers of the solvent species), the trend of this quantity as a function of the ratio of the jump frequencies of the components is in agreement with earlier numerical calculations for both f.c.c. and b.c.c. lattice models. Anomalously in our view, the trend predicted by some more recent numerical calculations [S. Ishioka and M. Koiwa, Phil. Mag. A50, 505 (1984)] is in the opposite sense.