Theory of the diffusion of heavy impurities in alkali metals

Abstract

Interatomic potentials have been developed for heavy atom impurities in alkali metal hosts, and they have been used to calculate characteristic energies for the diffusion of gold in sodium and of silver in lithium. The calculations show that, whilst most impurity atoms should be present substitutionally, the diffusion is dominated by interstitial motion for both Li-Ag and Na-Au. The large difference in observed behaviour stems from the different forms of the interatomic potentials but cannot be described simply in terms of atomic radii or electronegativity arguments. The activation energies predicted are in good quantitative agreement with experiment.