Defects in Metals

Abstract

Abstract Isolated impurity atoms in an otherwise perfect metallic crystal form point defects in the crystals. Heavy atoms enter the host metal lattices substitutionally, and the point symmetry at such sites is the same as that for the host atoms. The EFGs at the nuclei of impurity atoms depend on the local electronic structure around these centres as well as on the symmetry and distances to the charged ion cores in the host crystal. Therefore data on EFGs contain implicit information on the electronic structure of the point defects. EFGs at point defects cannot be straightforwardly predicted from the parameters determined in a usual band-structure calculation, since such a calculation would require a detailed knowledge of the wave functions in the vicinity of the impurity atom. A theoretical approach based on a simulation of the ‘impurity plus nearest host metal atoms’ by a sufficiently large molecular cluster is a more appropriate basis for predictions of impurity EFGs and has been attempted in a few cases (Lindgren 1986). However, most of the comparison between experimental data and theory is still at a much less ambitious level. Since the experimental data are of fairly high accuracy, they can be said to form a future resource for testing electronic structure calculations for impurities in metals-a topic of considerable interest for materials science.