This theory predicted a so-called effective valence, for solute impurities, by assuming that the bulk valences of the solvent and solute metals were those given by the Engel-Brewer theory (unity for body-centered cubic structures, 2 for hexagonal close-packed structures, 3 for face-centered cubic structures). The effects of balancing the Fermi energy level of the solute with that of the solvent, and differences in zero-point energy, were considered when calculating the effective valence. The latter was then used to deduce the activation energy for diffusion by using a modified Lazarus-LeClaire approach. It was shown that the proposed theory worked well for the impurity diffusion of a number of solutes in Al, Cu, Ga, Ag, Pb, and Sn.

J.R.Cahoon: Metallurgical and Materials Transactions A, 1997, 28[3], 583-93