Transições de fase no LiCsSO4

Abstract

In this work we studied LiCsso4 crystals by measuring dielectric constant and obtaining Raman polarized spectra as a function of temperature in the range 15K-300K. The dependence of the dielectric constant on the frequency as well as the dependence of the Raman Spectra with the geometry of scattering were studied. These measurements were done for each degree in the range from 195K to 210K. We were interested in measuring the transition temperature in this interwal to solve some ambiguities between the proposal of Kruglik et al and Ribeiro et al about the existence of an intermediate phase between 202K and 209K (Kruglik et al). We found a transition at 202K structure belonging to the talking from an orthorhombic D16 2h space group to a monoclinic structure. Results of the-Raman polarized scattering as a function of geometry sh9wed that this monoclinic phase has a center of inversion and its symmetry belongs to the space group. We identified and classified the normal frequencies of the medes that are Raman-active in both phases. We also showed that this transition of .. LiCsSO 4 is revertible, non-destructive, second-order, obeys the LandauLifshitz criteria and is ferro-elastic. The transition is trigered by the rotation of the so4 ions tetrahedra around the e axis, leading to motion of the oxygen ions in the X-Y plane and affecting mainly the XX,YY and XY polarization.