Dielectrics

IR-active phonons of the LiNbGeO$_5$ superionic crystal

V. A. Yakovlev^a, N. N. Novikova^a, A. D. Molchanova^a, V. A. Chernyshev^b, S. A. Klimin<sup>a

a</sup> Institute of Spectroscopy, Russian Academy of Sciences, Troitsk, Moscow, Russia
^b Ural Federal University named after the First President of Russia B. N. Yeltsin, Yekaterinburg, Russia

Abstract: The infrared (IR) reflectance spectra of the LiNbGeO$_5$ superionic crystal have been studied. The crystal belongs to the orthorhombic syngony, the space group $Pnma$. Measurements in polarized light made it possible to separate phonons by symmetry in accordance with the selection rules. The spectral dependences of the reflectivity $R(\nu)$ for three polarizations along the crystallographic axes were modeled using dispersion analysis. The parameters of IR-active phonons of symmetry $B_{1u}$, $B_{2u}$ and $B_{3u}$ are obtained. A group-theoretical analysis of the vibrational spectrum has been performed. The frequency dependences of the complex dielectric constant and the loss function are calculated. The frequencies of IR-active phonons are calculated from the first principles. The experimental and calculated frequencies of IR-active phonons are close to each other. Inverted phonons have been detected.

Keywords: LiNbGeO$_5$, IR reflection spectroscopy, dispersion analysis, first principles calculation, group-theoretic analysis.

Received: 24.04.2024
Revised: 24.04.2024
Accepted: 20.05.2024

DOI: 10.61011/FTT.2024.06.58255.103

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