Electric-Field Gradient Characterization at 181Ta Impurities in Sapphire Single Crystals

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

La Habana

Simposio; Simposio Latinoamericano de Física del Estado Sólido (SLAFES 2004), 6 al 9 de Diciembre de 2004,; 2004

SLAFES

In the last few years, electronic structure ab initio methods within the framework of theDensity Functional Theory (DFT), like the Full-Potential Linearized-Augmentd Plane-Waves(FP-LAPW) method, have been applied for the first time to doped semiconductors [1] and, inparticular, to semiconductor oxides with diluted impurities [2]. These studies enable the description of very interesting structural and electronic properties in these impurity-hostsystems. Due to the very good description of the electronic charge density done by the FP-LAPW method, it enables at present the most accurate calculation of the electric-field gradient (EFG) tensor in a crystalline solid. In this work we show how Perturbed-Angular Correlation (PAC) experiments in single crystals (in which another physical quantity such as the EFG orientation can be measured) can be an adequate check of the approximations done in thesetheories. In this work we present PAC results of corundum Al2O3 single crystals implantedwith 181 Hf ions at the ISKP at Bonn and measured at La Plata with a high efficiency and time-resolution spectrometer. The magnitude, asymmetry, and orientation (with respect to thecrystalline axis) of the EFG tensor was determined measuring the spin-rotation curves as afunction of different orientations of the single crystals relative to the detector plane. Theseresults are analyzed in the framework of ab initio and point-charge model calculations, andalso with PAC results coming from experiments with 111 In/111 Cd impurities.[1] Lany et al., PRB 62, R2259 (2000).[2] Errico et al., PRL 89, 55503 (2002).