It was pointed out that fast solute diffusion in certain dilute binary alloys could be understood by using a modified version of Hägg’s rule. This method was confirmed, and was used to analyze published data on the fast diffusion of solutes (mainly 3d elements) in anisotropic host phases such as -U and -Zr. It was found that the activation enthalpy for fast diffusion consisted of elastic contributions, which were related to the Hägg parameter, and of a chemical one which was due to electronic solute-solvent interactions. In the case of Fe, Co, Ni and O in -Zr, the chemical contribution could be deduced from the relevant solute-host phase diagrams. The Hägg approach defined the geometrical framework within which fast solute diffusion occurred. It was concluded that it was somewhat complementary to the Miedema model, but the latter tended to neglect those structural details of the host lattice which were essential for interstitial diffusion.

H.Blank: Journal of Nuclear Materials, 1997, 240[3], 169-84