Hyperfine interactions at ¹⁸¹Hf(→¹⁸¹Ta) impurities implanted in Er₂O₃ and Gd₂O₃: structural and electronic dependence of the EFG in bixbyite sesquioxides

Abstract

The time-differential-perturbed γ-γ angular-correlation technique (TDPAC) with ion-implanted ¹⁸¹Hf tracers has been applied to study the hyperfine interactions of ¹⁸¹Ta impurities in the cubic bixbyite structure of Er₂O₃ and Gd₂O₃. The TDPAC experiments were performed in air in the temperature range 300-1073 K (in the case of Er₂O₃) and 300-1173 K (in the case of Gd₂O₃). 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 (EFG) acting on ¹⁸¹Ta 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 ¹¹¹Cd and ¹⁸¹Ta in other isomorphous sesquioxides. The temperature dependence of the hyperfine parameters for both oxides is also discussed in terms of dilatometric expansion data.