Crystal structure and phase transitions of a layered perovskite-like CsScF4 crystal

Abstract

This work is devoted to the complex research on temperature phase transitions in a CsScF₄ crystal. The crystal structure was solved and refined at different temperatures by using the Rietveld method. Structural phase transitions were investigated by using the following spectroscopic methods, some of them for the first time: Brillouin spectroscopy, Raman spectroscopy, IR absorption spectroscopy and NMR. The symmetry analysis of the Brillouin zone center of all phases is presented. The vibrational spectra of the crystal in three phases have been calculated. The structural phase transition mechanism was determined. The transitions at T₁ = 475 K and T₂ = 317.5 K are of displacement type. The Raman soft modes have been associated with rotations of the ScF₆ octahedral group.