Berlin 2008 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 7: Point defect spectroscopy and engeneering

DF 7.2: Hauptvortrag

Dienstag, 26. Februar 2008, 10:40–11:20, EB 107

Polarons in lithium niobate — •Ortwin Schirmer — FB Physik, Universität Osnabrück

LiNbO₃ is an extraordinary testing ground for various manifestations of polarons. The Li-substoichiometry of its congruently melting composition facilitates the formation of bound hole (O⁻), bound single electron (Nb_Li⁴⁺) and bound electron bi-polarons (Nb_Li⁴⁺ - Nb_Nb⁴⁺). Also free electron polarons (Nb_Nb⁴⁺) can be prepared. In all cases these polarons are small, i.e. the ranges of the carrier amplitude and related lattice distortions extend over about one bond length. On the basis of detailed experimental information on bound hole polarons in numerous oxide materials, methods established for color centers have recently been modified to interpret the details of the corresponding strong optical absorption bands. This approach is extended to electron polarons in LiNbO₃. It allows to understand the related phenomena, most of them known since a long time, from a common viewpoint. Among the treated features will be the interpretation of the peak energies and shapes of the optical absorption bands, the binding energies of bipolarons as well as their dissociation and recombination.