Hyperfine interactions at ~(181)Hf(→~(181)Ta) impurities implanted in Er_2O_3 and Gd_2O_3: structural and electronic dependence of the EFG in bixbyite sesquioxides

摘要

The time-differential-perturbed γ-γ angular-correlation technique (TDPAC) with ion-implanted ~(181)Hf tracers has been applied to study the hyperfine interactions of ~(181)Ta impurities in the cubic bixbyite structure of Er_2O_3 and Gd_2O_3. The TDPAC experiments were performed in air in the temperature range 300-1073 K (in the case of Er_2O_3) and 300-1173 K (in the case of Gd_2O_3). Three electrical-quadrupole interactions were found in each oxide in the whole studied temperature range. Two of them were attributed to the electric-field gradients (EFC) acting on ~(181)Ta probes substitutionally located on the two nonequivalent free-of-defects cation sites of the bixbyite structure. The EFG results are compared with predictions of the point-charge model and discussed together with previous results obtained with the probes ~(111)Cd and ~(181)Ta in other isomorphous sesquioxides. The temperature dependence of the hyperfine parameters for both oxides is also discussed in terms of dilatometric expansion data.