Electric field gradients in nonmagnetic dilute alloys of aluminum and copper

Abstract

The electric field gradient (EFG) and the asymmetry parameter ($\ensuremath{\eta}$) are investigated at the first-, second, third-, and fourth-nearest-neighbor (NN) sites for nonmagnetic dilute alloys of Al and Cu. The impurity effective valency is calculated according to the Friedel criterion of bound states. The impurity-induced electronic charge density is calculated self-consistently in the Hohenberg-Kohn-Sham density-functional formalism and is used to evaluate the valence-effect contribution to the EFG. The size-effect contribution to the EFG is estimated in the elastic continuum model. Reliable values of the core-enhancement and Sternheimer antishielding factors are used. No size-strength parameter is introduced to explain the EFG's at the 2NN, 3NN, and 4NN sites. However, the EFG's at the 1NN site are explained with the help of a size-strength parameter ${C}^{\ensuremath{'}}$ which accounts for the deficiency of the elastic continuum model. The calculated values of EFG and are $\ensuremath{\eta}$ found to be in reasonable agreement with the experimental values for most of the alloys. In Al alloys the size-effect EFG is found to be dominant at the 1NN site and the valence-effect EFG is found to be dominant at the 2NN, 3NN, and 4NN sites. In Cu alloys the size-effect EFG is dominant at all the NN sites.