Hyperfine interactions in the cubic phase of BaTixHf1-xO3

The hyperfine quadrupole interaction at probes in sites with cubic point group symmetry was measured in many perovskite-type compounds. This interaction is commonly associated to the presence of oxygen vacancies close to probes. The effect of this point defect on Ta-181 probe in BaTi x Hf1-xO3 for x = 0.70, 0.50, 0.30, 0.10, 0.05, and 0.01, is studied. The lattice constant of these oxides at room temperature were measured using XRD technique. The quadrupole parameters corresponding to probe-defect interaction were obtained by means of Perturbed Angular Correlation (PAC) spectroscopy as functions of both, composition and temperature. A static, asymmetric and distributed quadrupole interaction was fitted to all PAC data. This interaction was observed to be strongly composition dependent. These results and those corresponding to compositions 0.75 less than or equal to x < 1 were compared to the ones obtained using the point charge method for the calculation of the electric field gradient. The proposed model took into account polarized oxygen vacancies, different covalence of Ti-O and Hf-O bonds and using computational simulation for cations and oxygen vacancies lattice positions.