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Calculations of the Electronic and Atomic Structure and Diffusion of Point Defects in KNbO3 Perovskite Crystals and Relevant KTN Solid Solutions

Published online by Cambridge University Press:  01 February 2011

R. I. Eglitis ,
E. A. Kotomin  and
G. Borstel
R. I. Eglitis
Affiliation:
Department of Physics, University of Osnabrueck, D-49069 Osnabrueck, Germany
E. A. Kotomin
Affiliation:
Department of Physics, University of Osnabrueck, D-49069 Osnabrueck, Germany Institute of Solid State Physics, University of Latvia, 8 Kengaraga str., Riga LV-1063, Latvia
G. Borstel
Affiliation:
Department of Physics, University of Osnabrueck, D-49069 Osnabrueck, Germany
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Abstract

In this paper we review our recent achievements in large scale computer simulations of point defects in advanced perovskite crystals. We have calculated the defect migration energies in the KNbO3 cubic phase using quantum chemical method of the Intermediate Neglect of Differential Overlap (INDO) and classical shell model (SM). The migration energies for the O vacancy obtained by means of these two quite different methods are reasonably close (0.68 eV and 0.79 eV, respectively) and also agree with the only experimental estimate available (ca. 1 eV). Atomic relaxations calculated by these two methods also agree quite well. We used INDO method for a large-scale modeling of the atomic and electronic structure of KNbxTa1-xO3 (KTN) perovskite solid solutions. Results for periodic defect model (large unit cell) of 40 and 320 atoms are compared with 135-atom INDO cluster calculations. Periodic Nb impurities in KTaO3 reveal clear off-center displacement beginning with the smallest calculated concentrations, so does an isolated Nb impurity in a cluster INDO calculation. The magnitude of this displacement is close to the EXAFS observation (0.27 a.u.).

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 718: Symposium D – Perovskite Materials , 2002 , D11.11
Copyright
Copyright © Materials Research Society 2002

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