The enhancement of solvent as well as solute diffusion is discussed for substitutional alloys with impurities of positive excess charge as a function of composition and temperature. The enhancement factors of solvent diffusion up to third order in the impurity concentration and the corresponding enhancement factors of solute diffusion up to second order are calculated in terms of the complex model of Dorn and Mitchell and its application to diffusion introduced by Hehenkamp et al. The binding free enthalpies of the different vacancy-impurity complexes and the impurity-impurity interaction energies are calculated from these quantities, without resorting to further assumptions as in former treatments. This formalism is applied to AgSn and AgSb alloys. Employing a modified rigid-band model of Friedel, together with measurements of the nuclear Knight shift, we find the complex model to be applicable far beyond the range of infinite dilution. As for noble metals, it applies quantitatively up to solute concentrations of about 5 at.?and, at least qualitatively, for alloys with even higher concentrations.

• Received 6 March 1986

DOI:https://doi.org/10.1103/PhysRevB.34.2116