Journal of Physical Studies 22(2), Article 2701 [5 pages] (2018) DOI: https://doi.org/10.30970/jps.22.2701 LATTICE VIBRATION SPECTRA OF A4BX6 GROUP CRYSTALS A. I. Kashuba{1,2}, M. V. Solovyov{1}, T. S. Maliy{1}, I. A. Franiv{3}, O. O. Gomonnai{4}, O. V. Bovgyra{1}, O. V. Futey{2}, A. V. Franiv{1}, V. B. Stakhura{1} {1}Physics Faculty, Ivan Franko National University of Lviv 8, Kyrylo and Mefodiy St., Lviv, UA-79005, Ukraine {2}Electronics and Computer Technology Faculty, Ivan Franko National University of Lviv 107, Tarnavski St., Lviv, UA-79017, Ukraine {3}Lviv Polytechnic National University, 12, Bandera St., Lviv, UA-79013, Ukraine {4}Physics Faculty, Uzhgorod National University, 54, Voloshina St., Uzhgorod, UA-88000, Ukraine e-mail: MVSolovyov@ukr.net

We report on an X-ray diffraction study of $A_{4}BX_{6}$ (Tl$_{4}$HgI$_{6}$ and Tl$_{4}$CdI$_{6}$) group crystals. Structure data and atomic coordinates have been obtained by Rietveld method. The compounds of Tl$_{4}$HgI$_{6}$ and Tl$_{4}$CdI$_{6}$ are isomorphous with each other and crystallize in a tetragonal lattice with the space group of \textit{P}4/\textit{mnc}. The results of the infrared and Raman spectra of Tl$_{4}$HgI$_{6}$ and Tl$_{4}$CdI$_{6}$ crystals are present. On the basis of a factor group analysis and phonon frequencies calculated for Tl$_{4}$HgI$_{6}$ and Tl$_{4}$CdI$_{6}$, the relations between the vibrational spectra and the crystal structures have been determined. Moreover, the distribution of vibrations for symmetry classes of single crystals and the selection rules for vibrations in the infrared absorption and Raman spectra are obtained. Phonon modes frequencies and their origin determination are based on Raman scattering data.

PACS number(s): 78.30.-j

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