Electric-Field Gradient Characterization at 181Ta Impurities in Sapphire SingleCrystals

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

La Habana, Cuba

Simposio; XVII Latin American Symposium on Solid State Physics (SLAFES 2004); 2004

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In the last few years, electronic structure ab initio methods within the framework of the Density 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, in particular, to semiconductor oxides with diluted impurities [2]. These studies enable the description of very interesting structural and electronic properties in these impurity-host systems. 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 these theories. In this work we present PAC results of corundum Al2O3 single crystals implanted with 181Hf 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 the crystalline axis) of the EFG tensor was determined measuring the spin-rotation curves as a function of different orientations of the single crystals relative to the detector plane.  These results are analyzed in the framework of ab initio and point-charge model  calculations, and also with PAC results coming from experiments with 111In/111Cd impurities.   [1] Lany et al., PRB 62, R2259 (2000). [2] Errico et al., PRL 89, 55503 (2002).