Quantum chemical modelling of point defects in KNbO3 perovskite crystals

Autor(en): Kotomin, EA
Eglitis, RI
Borstel, G
Stichwörter: AB-INITIO; ALKALINE-EARTH OXIDES; CORUNDUM CRYSTALS; DOPED KTAO3; ELECTRONIC-STRUCTURE; F-CENTERS; HARTREE-FOCK CALCULATIONS; Materials Science; Materials Science, Multidisciplinary; OPTICAL-PROPERTIES; perovskite ferroelectrics; phase transitions; point defect; polaron; SEMIEMPIRICAL CALCULATIONS; SOLID-SOLUTIONS
Erscheinungsdatum: 2000
Volumen: 17
Ausgabe: 2-4
Startseite: 290
Seitenende: 298
We present results of semi-empirical quantum chemical calculations for several perovskite KNbxTa1-xO3 (KTN) solid solutions, as well as point intrinsic defects - F centers and hole polarons bound to K vacancy - in KNbO3. Method of the intermediate neglect of the differential overlap (INDO) was combined with typically 320-atom supercells and atomic geometry optimization. Analysis of the optimized atomic and electronic structure has clearly demonstrated that several nearest Nb atoms substituting for Ta in KTaO3 - unlike Ta impurities in KNbO3 - reveal the self-ordering effect, which probably triggers the ferroelectricity observed in KTN. We predict co-existence of one-site (atomic) and two-site (molecular) polarons with close absorption energies (approximate to 1 eV). When available, the INDO results are compared with ab initio calculations. The relevant experimental data art discussed. (C) 2000 Elsevier Science B.V. All rights reserved.
Spring Meeting of the European-Materials-Research-Society, STRASBOURG, FRANCE, JUN 01-04, 1999
ISSN: 09270256
DOI: 10.1016/S0927-0256(00)00040-9

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