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Theoretical Prediction and Experimental Confirmation of Charge Transfer Vibronic Excitons and Their Phase in ABO3 Perovskite Crystals

Published online by Cambridge University Press:  01 February 2011

R. I. Eglitis ,
V. S. Vikhnin ,
E. A. Kotomin ,
S. E. Kapphan  and
G. Borstel
R. I. Eglitis
Affiliation:
Department of Physics, University of Osnabrueck, D-49069 Osnabrueck, Germany
V. S. Vikhnin
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
S. E. Kapphan
Affiliation:
Department of Physics, University of Osnabrueck, D-49069 Osnabrueck, Germany
G. Borstel
Affiliation:
Department of Physics, University of Osnabrueck, D-49069 Osnabrueck, Germany
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Abstract

The current theoretical and experimental knowledge of new polaronic-type excitons in ferroelectric oxides - charge transfer vibronic excitons (CTVE) is discussed. It is shown that quantum chemical Hartree-Fock-type calculations using a semiempirical Intermediate Neglect of Differential Overlap (INDO) method (modified for ionic/partly ionic solids) as well as photoluminescence studies in ferroelectric oxygen-octahedral perovskites confirm the CTVE existence. Our INDO calculations for KTaO3 and KNbO3 have demonstrated that the triplet exciton is a triad centre containing one active O atom and two Ta atoms sitting on the opposite sites from this O atom. The total energy of a system is lowered by the combination of Coulomb attraction between electron and hole and the vibronic effect in this charge transfer vibronic exciton. It is shown by means of our INDO calculations that polaronic-type CTVE in ferroelectric oxides could lead to the formation of a new crystalline phase. The ground state energy of this phase consisting of strongly correlated CTVEs lies within an optical gap of a pure crystal, and is characterized by a strong tetragonal lattice distortion, as well as by the ferroelectric ordering.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 718: Symposium D – Perovskite Materials , 2002 , D10.32
Copyright
Copyright © Materials Research Society 2002

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