SKM 2021 – scientific programme

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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 5: Poster Session KFM

KFM 5.7: Poster

Tuesday, September 28, 2021, 16:00–17:00, P

Vibrational properties of strained LiNbO₃ and LiTaO₃ crystals — •Mike Nico Pionteck and Simone Sanna — Institut für Theoretische Physik and Center for Materials Research, Justus-Liebig-Universität Gießen, 35392 Gießen, Germany

The investigation of Raman frequencies is a widely used non-destructive way to characterize crystalline solids and nanostructures. X-ray diffraction measurements have shown that domain walls in LiNbO₃ and LiTaO₃ behave like compressed bulk material [1]. Hence, knowledge of the dependence of Raman frequencies on uniaxial strain can help, i.a., to characterize domain walls in LiNbO₃ and LiTaO₃ crystals.

In our work, we model the vibrational properties of LiNbO₃ and LiTaO₃ crystals from first principles as a function of compressive and tensile strain in x-, y- and z-direction. The calculations show a roughly linear dependence of the phonon frequencies on the applied strain, which is similar for LiNbO₃ and LiTaO₃ crystals. The frequencies increase linearly under compressive strain. On the other hand, they decrease linearly under tensile strain. In particular, we observe a strong dependence on strain in x- and y-direction for the E TO₅ and TO₆ modes which can be thus exploited as markers of the strain. While E modes of unstrained LiNbO₃ and LiTaO₃ crystals are degenerate [2], we predict non-degenerate E modes under strain, due to the breaking of rotational symmetry by strain in x- and y-direction. [1] M. Rüsing et al., Phys. Rev. Mat. 2, 103801 (2018). [2] S. Sanna et al., Phys. Rev. B 91, 224302 (2015).