PAC experiments at impurity sites in synglecrystals: checking electronic structure ab initio calculations in doped-semiconductors

M. RENTERÍA; G. N. DARRIBA; L. A. ERRICO; P. D. EVERSHEIM

Bonn, Alemania.

Conferencia; XIII International Conference on Hyperfine Interactions and XVII Internacional Symposium on Nuclear Cuadrupole Interactions; 2004

Recently,  ab initio electronic structure calculation methods in the framework of the Density Functional Theory (DFT), like the “Full-Potential Linearized Augmented Plane Wave” (LAPW),   have been  applied for the first time to doped semiconductors and, in particular , to oxide semiconductors with diluted impurities, enabling the description  of structural and electronic properties of these complex systems. The LAPW method is one of the more accurate methods at present to calculate the electric-field gradient (EFG), due to the very good description of the electronic density near the probe-nucleus. In this work we show how g-g Perturbed-Angular-Correlation (PAC) experiments are an excellent test of the approximations used in DFT. In particular, we present PAC results in TiO2 synglecrystals  implanted with 181Hf ions at the ISKP and measured at La Plata with a high resolution and efficiency fast-fast spectrometer, in the temperature range RT-1273 K. The magnitude, asymmetry, and orientation of the measured EFG tensor at Ta sites with respect to the TiO2 crystal axis are compared with the first ab initio calculations at Ta impurities in an oxide, TiO2, and to experimental and theoretical results at Cd and Ti sites in TiO2. The confidence obtained for the theoretical calculations enables the determination of the EFG sign, not affordable with conventional PAC experiments.