Electric field gradient in dilute transitional alloys of Cu and Al

An attempt is made to explain the electric field gradient (EFG) and the asymmetry parameter η for Cu alloys with Ni, Pd, and Pt impurities and Al alloys with Sc, Ti, V, Cr, Mn, Fe, and Cu impurities. In Cu alloys, the valence effect contribution to the EFG is estimated using the Alfred and Van Ostenburg charge perturbation theory and the size effect contribution is adopted from that by Sagalyn and Alexander. Leading phase shifts are assumed to be η0 and η2 and these are determined by satisfying experimental data for residual resistivity and the Friedel sum rule. The effective charge on the impurity is estimated using the Friedel criterion of the bound state. It is found that the EFG increases with an increase in effective charge on the impurity. The size effect contribution dominates over the valence effect contribution. The agreement between the calculated and experimental values of the EFG and η for CuNi, CuPd, and CuPt is reasonably good. The calculations for the EFG and η for Al alloys are carried out following the charge perturbation theory due to Lautenschlager and Mrosan where the preasymptotic contribution is explicitly included through the energy dependence of phase shifts. Except for AlFe, the size effect contribution is greater than the valence effect contribution. The calculated and experimental values of the EFG and η are in reasonable agreement except for AlSc. Possible reasons for this are discussed.