Spectroscopy of condensed matter

Spectra of infrared reflection and Raman scattering of light of crystals with a belousovite structure from first principles

Yu. N. Zhuravlev

Kemerovo State University, Kemerovo, Russia

Abstract: In the full-electron and pseudopotential basis of localized atomic orbitals with the exchange-correlation functional PBE and the dispersion correction D3 of the CRYSTAL code, the crystal structure, dielectric constant tensor, LO–TO mode splitting, infrared reflection spectra and Raman scattering of the mineral belousovite and its synthetic analogues with formula AZnSO$_4$X (A = K, Rb, Cs, Tl; X = Cl, Br, I). The presence of SO$_4$, ZnO$_3$X tetrahedra and AO$_n$X$_m$ polyhedra in the structure is shown, which appear in different regions of the vibrational spectra. In polarized reflection spectra, SO$_4$ modes have high-intensity bands $\nu_1$ and $\nu_3$ from 900 to 1160 cm$^{-1}$, formed by vibrations of nonequivalent oxygen atoms. In the lattice region below 150 cm$^{-1}$, vibrations involving cation atoms are distinguished. Individual modes with a high level of LO–TO splitting have been identified. In the Raman spectrum, the most intense modes will also be $\nu_1$, $\nu_3$. The first group consists of four modes, where the most intense one at 900–920 cm$^{-1}$ is formed largely by vibrations of individual nonequivalent oxygen atoms, and the other three by sulfur atoms and other atoms. On the contrary, modes with wavenumbers above 1100 cm$^{-1}$ have an overwhelming contribution from O4 oxygen atoms with the shortest S-O and A-O distances. For these and other modes, linear dependences of wave numbers on interatomic distances, average atomic masses and radii of cations A and anions X have been established.

Keywords: belousovite, synthetic crystals, ab initio, dielectric constant, infrared reflectance spectra, Raman spectra.

Received: 03.07.2024
Revised: 26.08.2024
Accepted: 27.08.2024

DOI: 10.61011/OS.2024.08.59035.6851-24

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