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

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

Bonn

Conferencia; 13th International Conference on Hyperfine Interactions & 17th International Symposium on Nuclear Quadrupole Interaction; 2004

ISKP, Bonn, Germany

Recently, ab initio electronic structure calculation methods in the framework of theDensity Functional Theory (DFT), like the “Full-Potential Linearized Augmented PlaneWave” (LAPW), have been applied for the first time to doped semiconductors and, inparticular , to oxide semiconductors with diluted impurities, enabling the description ofstructural and electronic properties of these complex systems. The LAPW method is oneof 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 - Perturbed-Angular-Correlation (PAC) experiments are anexcellent test of the approximations used in DFT. In particular, we present PAC resultsin TiO2 synglecrystals implanted with 181 Hf ions at the ISKP and measured at La Platawith a high resolution and efficiency fast-fast spectrometer, in the temperature rangeRT-1273 K. The magnitude, asymmetry, and orientation of the measured EFG tensor atTa sites with respect to the TiO2 crystal axis are compared with the first ab initiocalculations at Ta impurities in an oxide, TiO2, and to experimental and theoreticalresults at Cd and Ti sites in TiO2. The confidence obtained for the theoreticalcalculations enables the determination of the EFG sign, not affordable withconventional PAC experiments.This research was partially supported by CONICET, Fundación Antorchas,ANPCyT (PICT 03-03727), Argentina, and TWAS, Italy. MR (GND and LAE) is (are)member (fellows) of CONICET, Argentina.