DARRIBA German Nicolas
First-principles and time-differential gamma-gamma perturbed?angular-correlation spectroscopy study of structural and electronic properties of Ta-doped TiO2 semiconductor
G. N. DARRIBA; L. A. ERRICO; P. D. EVERSHEIM; G. FABRICIUS; M. RENTER¨ªA
PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS
Año: 2009 vol. 79 p. 115213 - 115213
The, time-differential gamma-gamma perturbed-angular-correlation TDPAC technique using ion-implanted 181Hf →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 300?1273 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 were performed 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 with conventional 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.