CONICET | Buscador de Institutos y Recursos Humanos

La pagina inicial es 115213-1 y la final 115213-12 (12 paginas en total) The, time-differential perturbed-angular-correlation (TDPAC) technique using ion-implanted181Hf->181Ta tracers was applied to study the hyperfine interactions of 181Ta impurities in the rutile structure of TiO2 single crystals. The experiments were performed in air in the temperature range of 3001273 K, allowing the electric-field-gradient (EFG) tensor characterization in magnitude, asymmetry, and orientation at 181Ta probe atoms located in defect-free cation sites of the structure. The measured EFG is parallel to the (001) crystal axis, as occurs at Ti sites, but normal to the EFG orientation observed at 111Cd impurities in TiO2 single crystals (L. A. Errico et al., Phys. Rev. Lett. 89, 055503 (2002)). In addition, ab initio calculations wereperformed using the full-potential augmented plane wave plus local orbital method that allow us to treat the electronic structure of the doped system and the atomic relaxations induced by the Ta impurity in a fully self-consistent way. We considered different dilutions of the doped system (using the supercell approach) and studied the electronic properties and structural atomic relaxation dependence on the charge state of the impurity. The accuracy of the calculations and the excellent agreement of the predicted magnitude, asymmetry, and orientation of the EFG tensor with the experimental results enable us to infer the EFG sign, not accessible withconventional TDPAC experiments. The comparison of the measured EFG at Ta sites with experimental and ab initio theoretical results reported in the literature at Cd, Ta, and Ti sites in TiO2 allowed us to obtain a deeper insight on the role played by metal impurities in oxide semiconductors.