Perturbed-angular-correlation study of the electric-field gradient in 181Hf-doped and implanted indium sesquioxide

We studied the hyperfine interactions of 181Ta in In2O3 by means of perturbed-angular-correlation (PAC) measurements. We prepared thin films of indium sesquioxide with different degrees of initial amorphism and implanted them with 181Hf. Chemically prepared indium-sesquioxide powder samples were also made starting from neutron-irradiated HfCl4, which provides the 181Hf PAC probes. PAC experiments were performed on each sample at room temperature, after each step of annealing programs at increasing temperatures up to the full crystallization of the samples. The results indicate that the PAC probe occupies preferentially the axially symmetric cation site. Point-charge-model calculations were performed. The calculated asymmetry parameters η were compared with those obtained in 181Hf PAC experiments performed also on other binary oxides, showing that the symmetry of the electric-field-gradient (EFG) tensor at 181Ta cation sites in binary oxides is mainly determined by the nearest-neighbor oxygen-ion distribution around the probe. Comparisons of the experimental results in bixbyites obtained for both PAC probes, 111Cd and 181Ta, show that the local EFG in bixbyites, are strongly dependent on the geometry of the sites and the electronic configuration of the probes. copyright 1997 The American Physical Society