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Dresden 2003 – scientific programme

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DF: Dielektrische Festkörper

DF 2: Elektrische und optische Eigenschaften II

DF 2.7: Talk

Monday, March 24, 2003, 16:50–17:10, HSZ/403

Lattice dynamics in LiNbO3 and LiTaO3 — •Andrei Postnikov1, Vasile Caciuc1,2, Patrice Bourson3, and Marc Fontana31Universität Osnabrück – Fachbereich Physik, 49069 Osnabrück — 2Institut für Festkörperforschung – Forschungszentrum Jülich, 52425 Jülich — 3MOPS-CLOES, Supélec, 2 rue E.Belin, F-57070 Metz Cedex, France

Zone-center phonons in ferroelectric lithium niobate are discussed in comparison with lithium tantalate. Despite the similarities in crystalline and electronic structure of these materials, the shifts in the positions of their Raman lines cannot be trivially related to differences in Nb/Ta masses. Instead, they can be traced back to different compositions of (some) eigenvectors, estimated from first-principles total-energy calculations. For stoichiometric substances, frozen-phonon calculations done with the full-potential linearized augmented plane wave method (WIEN97) help to obtain the eigenvectors of the transversal optical E-modes in LiTaO3, to be compared with earlier obtained results on LiNbO3. For LiNbO3, the use of numerical orbital tight-binding method (SIESTA) allows to try enlarged unit cells and address the issues of phonon dispersion, intrinsic defects (almost unavoidable in this material), and anharmonicity.

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