A comparative study of the atomic and electronic structure of F centers in ferroelectric KNbO3: Ab initio and semi-empirical calculations

Autor(en): Kotomin, EA
Christensen, NE
Eglitis, RI
Borstel, G
Stichwörter: 1ST-PRINCIPLES CALCULATIONS; ab initio; CORUNDUM CRYSTALS; defects; F center; ferroelectrics; FIRST-PRINCIPLES CALCULATIONS; IONIC-CRYSTALS; KNbO3; KTAO3; LITHIUM-NIOBATE; Materials Science; Materials Science, Multidisciplinary; OPTICAL-PROPERTIES; OXYGEN VACANCY; PEROVSKITE FAMILY; POINT-DEFECTS; quantum chemistry
Erscheinungsdatum: 1998
Herausgeber: ELSEVIER SCIENCE BV
Journal: COMPUTATIONAL MATERIALS SCIENCE
Volumen: 10
Ausgabe: 1-4
Startseite: 339
Seitenende: 345
Zusammenfassung: 
The linear muffin-tin-orbital method combined with density functional theory (in a local density approximation) and the semi-empirical method of the intermediate neglect of the differential overlap (INDO) based on the Hartree-Fock formalism are used for the supercell study of the F centers (O vacancy with two electrons) in cubic and orthorhombic ferroelectric KNbO3 crystals. The two electrons are found to be considerably delocalized even in the ground state of the defect. Their wave functions extend over the two Nb atoms closest to the O vacancy and over other nearby atoms. Thus, the F center in KNbO3 resembles much more electron defects in the partly covalent SiO2 crystal (the so-called E-1' center) rather than usual F centers in ionic crystals like MgO and alkali halides. This covalency is confirmed by the analysis of the electronic density distribution. The absorption energies were calculated by means of the INDO method using the Delta SCF scheme after a relaxation of atoms surrounding the F center. For the orthorhombic phase three absoprtion bands are predicted, the first one is close to that observed experimentally under electron irradiaton. Copyright (C) 1998 Elsevier Science B.V.
Beschreibung: 
Symposium on Computational Modeling of Issues in Materials Science at the International Conference on Applied Materials / European-Materials-Research-Society Meeting, STRASBOURG, FRANCE, JUN 16-20, 1997
ISSN: 09270256
DOI: 10.1016/S0927-0256(97)00134-1

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