Vtyurin А. N., Beluo А., Krylov А. S., Voronov V. N.

Raman spectra of Rb₂KScF₆ elpasolite crystal have been studied in a wide temperature range, including two transition points: from cubic to tetragonal, and then - to the monoclinic phase. For the first time both for this crystal and for fluoride elpasolites in general soft modes restoration has been found below transition points; in agreement with selection rules a splitting of degenerate modes has been observed as well both for lattice vibrations and internal modes of ScF₆ octahedrons. Parameters of Raman lines have been quantitatively analyzed and found in good agreement with known thermodynamic characteristics of these transitions; in particular, lines widths are shown to be determined by tree-phonons anharmonic interactions. A wide region of pretransitional fluctuations was found above the upper transition point.

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