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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).

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