R. J. C. Lima

High‐pressure Raman study of taurine crystal

Single-crystal samples of taurine, NH3C2H4SO3, were studied by Raman spectroscopy in a diamond-anvil cell up to pressures of 5.6 GPa. From the analysis of the results we observed that the crystal undergoes a phase transition at about 0.7 GPa. The transition is accompanied by the appearance of a phonon in the external mode region of the spectrum and by changes of both the wavenumber of the CCN bending and of the CSH torsional vibrations. Additionally evidence for a second phase transition occurring at 5.2 GPa was observed. Pressure coefficients for all modes observed in this work are also given. Copyright

A new phase in the LiRbSO4-LiCsSO4 system

In this work we have presented a spectroscopic study carried out to determine the room temperature crystal symmetry of LiCs0.5Rb0.5SO4 crystals. On the basis of x-ray and Raman scattering measurements, we have proposed that LiCs0.5Rb0.5SO4 crystallizes in a monoclinic structure belonging to the Cs point group with four molecules per unit cell, where the SO4 groups, Rb and Cs ions, are distributed into two non-equivalent C1(2) site symmetries.

Phase transition in an occupationally disordered sulfate system

Abstract We have investigated the behavior of the Li1.43Cs0.57SO4 single-crystal Raman spectra and dielectric permittivity as a function of temperature. It was observed that the crystal, which is an occupationally disordered system, with orthorhombic C2v2 structure at room temperature, undergoes a phase transition at 230xa0K. In the new phase the SO4 tetrahedra remain in two non-equivalent sites and there is no evidence of the doubling of the unit cell.