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KR: Fachgruppe Kristallographie

KR 5: Poster - Crystallography

KR 5.6: Poster

Mittwoch, 13. März 2013, 15:00–17:30, Poster B2

Optical characterization of the protonation and deprotonation of pyroelectric single crystals — •Thomas Köhler, Erik Mehner, Juliane Hanzig, Hartmut Stöcker, and Dirk C. Meyer — Institut für Experimentelle Physik, Technische Universität Bergakademie Freiberg, D-09596 Freiberg, Germany

Pyroelectric crystals are used in many optical devices, therefore, understanding of structural defects is essential. It is easy to incorporate hydrogen in air-grown LiNbO₃ and LiTaO₃, however, the exact processes are only partially understood. Hence, the incorporation of hydrogen in both materials was investigated via FT-IR and UV/VIS absorption spectroscopy. Specifically the hydrogen in the congruent crystals leads to OH absorption bands with two components at 3468 cm⁻¹, 3485 cm⁻¹ in LiNbO₃ and at 3463 cm⁻¹, 3481 cm⁻¹ in LiTaO₃, respectively.

It is observed that the OH bands decrease in reduced and increase in protonated and reprotonated crystals. A third component at about 3500 cm⁻¹ is discernible in the protonated LiNbO₃. Reduced crystals show no reprotonation – only in LiNbO₃ crystals deprotonated above 900 ^∘C the return of the OH band was observed. Furthermore, the varying degree of reduction of the samples has influence on the absorption in the visible range. A broad band is observed in heavily reduced crystals, which is assigned to the formation of polarons [1]. The formation of polarons is different in the two material systems and shows influence on their optical behavior and their defect structure.

[1] A. Dhar, A. Mansingh. J. Appl. Phys. 1990, 68 (11), 5804-5809.