Diffusion in order-disorder alloys. The face centered cubic AB 3 alloy

Abstract

Formulae for the order dependent part of the vacancy formation energies and migration energies have been derived for a Cu 3Au alloy using Kirkwood's theory. The vacancy formation energy for sites on the Au sublattice is strongly order dependent and larger than the energy for vacancy formation in the Cu sublattices. Explicit consideration of different types of jumps shows that diffusion in a Cu 3Au alloy below the critical temperature cannot be a random walk process. It is suggested that the activation energies determined in quenching experiments are determined by the activation energy of a jump of a Au atom and that this energy will be different from the activation energy for diffusion of Au atoms as determined in a diffusion experiment. Possible jump sequences for the Au and Cu atoms and an explanation for internal friction experiments are also suggested.