FP-LAPW study of structural and electronic properties of Cd-doped In2O3.

L.A. ERRICO, M. RENTERÍA, AND G. FABRICIUS

Bonn

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

ISKP, Bonn, Germany

The experimental study of nuclear-quadrupole interactions is often used as a powerfultool to obtain information about structural, electronic, and magnetic properties of solids. Inthe case of pure electric-quadrupole interactions, the measured quantities are the quadrupolecoupling constant nQ=eQVZZ/h (where VZZ is the principal component of the diagonalizedelectric-field gradient (EFG) tensor) and the asymmetry parameter h. The EFG is measuredvia its interaction with the nuclear-quadrupole moment Q of a suitable probe-atom bydifferent techniques, such as Perturbed-Angular Correlations (PAC). Generally, the probespecies is an impurity dopant, which is present in either trace or small amounts in the hostcrystal. For this reason, interpreting experimental results involves understanding chemicaldifferences between the probe atom and the indigenous ion for which the probe atomsubstitutes. As there is not a simple and accurate model to obtain the charge distribution fromknown experimental values of the EFG, approaches for a quantitative calculation of Vii areoften based on the point-charge model (PCM). Among the binary oxides, the sesquioxidesthat crystallize in the bixbyite structure were subject of several PAC investigations using111Cd as probe in the last ten years. In the past, and due to the large ionicities of these oxides,some authors claimed that PCM is accurate enough to describe the EFG in this class ofcompounds. We report in this contribution an ab-initio study of the bixbyite In2O3 dopedwith Cd impurities. Our study was performed with the WIEN97 implementation [1] of thefull-potential linearized-augmented-plane-wave (FP-LAPW) method. Due to the similaritybetween the indigenous cation (In) and the impurity (Cd) it was supposed in previous studiesthat the EFG can be investigated using PCM without taking into account lattice distortions orelectronic defect at the Cd site [2,3]. From our results (in good agreement with the EFGexperimental PAC datas ([2]), it is clear that previous hypothesis are incorrect. In effect, wefound that Cd impurities induces relaxations of about 5% in the Cd-ONN bonds. Concerningthe EFG, we found that PCM predict a contrary sign to those predict by FP-LAPW.Moreover, we found that the main contribution to the EFG is originated from Cd-5p electrons.This contribution is not take into account in the ionic PCM model.This work was partially supported by CONICET, Fundación Antorchas, andANPCyT (PICT98 03-03727), Argentina, and TWAS, Italy. L. A. E. is fellow ofCONICET. G.F. and M.R. are members of CONICET.[1] A. Bartos, K.P. Lieb, M. Uhrmacher, and D. Wiarda, Acta Cryst. B49(1993) 165.[2] D. Lupascu, A. Bartos, K. P. Lieb, and M. Uhrmacher, Z. Phys. B93(1994) 441.[3] P. Blaha, K. Schwarz, and J. Luitz, WIEN97 (K. Schwarz, T.U. Wien,Austria, 1999), ISBN 3- 9501031-0-4.