ELECTRIC-FIELD GRADIENT IN BINARY OXIDES AT THE CD-111 IMPURITY SITE

The electric-field gradient (EFG) at the probe-atom site in binary oxi des has been theoretically estimated, assuming it is composed of two t erms. The first term is local, due to deformation of the valence orbit als of the probe atom, and was calculated by methods of quantum chemis try. The second term is due to the rest of the lattice ions, and these were taken as point charges. In this work we found, for the well-know n Cd-111 probe, a correlation between the local and ionic contribution s to the EFG for the 29 oxides studied, which is very similar to the o ne deduced empirically from time-differential perturbed-angular-correl ation (TDPAC) experiments. Therefore, the hypothesis used to perform t hat empirical correlation is confirmed, i.e., both terms have differen t sign and the absolute value of the local contribution is larger than the ionic one in most cases.