SKM 2023 – wissenschaftliches Programm
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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 6: Poster
KFM 6.6: Poster
Dienstag, 28. März 2023, 17:00–19:00, P3
Vibrational and optical properties of LiNbO3 and LiTaO3 under uniaxial stress — •Mike Pionteck1, Ekta Singh2, Sven Reitzig2, Michael Lange2, Michael Rüsing2, Lukas Eng2, and Simone Sanna1 — 1Justus-Liebig-Universität Gießen, Germany — 2Technische Universität Dresden, Germany
In ferroelectrics, the bulk material and the domain walls differ strongly in their vibrational and optical properties. X-ray measurements have shown that the domain walls of LiNbO3 and LiTaO3 exhibit the structure of compressed bulk material [1]. Consequently, the knowledge of the Raman frequencies as well as the optical response of the bulk material as a function of stress can help to characterize the domain walls.
Our work provides, for the first time, a theoretical description of phonon frequencies under uniaxial stress along Cartesian axes using density functional theory (DFT). The calculations show a roughly linear dependence of the Raman frequencies on the applied stress, which is confirmed by corresponding Raman measurements. This behavior is very similar for LiNbO3 and LiTaO3 crystals. In particular, the E TO5 and TO6 modes show a strong dependence on uniaxial stress in the x and y direction. As the strain reduces the symmetry of the crystal, we predict degeneracy lifting for the E modes. In addition, we have calculated the linear and nonlinear optical behavior of LiNbO3. In particular, this includes the second (SHG) and third harmonic generation (THG) coefficients as a function of the applied uniaxial strain. [1] M. Rüsing et al., Phys. Rev. Mat. 2, 103801 (2018).