Electric field gradients of¹¹¹Cd in monoclinic (B-phase) rare earth sesquioxides

Abstract

Perturbed gamma - gamma angular correlation measurements with 111In(EC) 111Cd probes have been performed in the monoclinic (B-phase) rare earth sesquioxides Sm2O3, Eu2O3 and Gd2O3. The spectra in all three oxides show a dominating electric field gradient of high asymmetry, eta approximately=1, and strong coupling constant, nu Q approximately=208 MHz, at room temperature. A slight modification of the structure in this phase with temperature was observed, but no phase transition occurred. Unlike the other structural isomorphs of the rare earth oxides, the cationic lattice sites in the B phase are not equally occupied by the implanted 111In ions in the temperature range investigated (10-900 K). The point-charge model and symmetry considerations were used to associate the dominating electric field gradient with substitutional 111In on the crystallographic site M(3). Two additional electric field gradients populated in small fractions were found in limited temperature ranges and tentatively attributed to defects.