VIBRATIONAL STUDY OF THE PROTONIC SUPERIONIC CONDUCTOR CS5H3(SO4)4-CENTER-DOT-H2O

Infrared and Raman spectra of Cs5H3(SO4)4.H2O have been investigated i n the 4000-10 cm-1 region between 450 and 90 K. An assignment of bands in terms of OH group, distorted sulphate ion and crystalline water gr oup frequencies is proposed. One phase transition is observed at 415 K on heating and the spectral changes which occur between 150 and 240 K have been explained by progressive freezing out of the dynamically di sordered acid hydrogen bonds and rotationally disordered water molecul es on cooling. The spectroscopic results are compared with dielectric relaxation and NMR measurements on Cs5H3(SO4)4.H2O as well as with cry stallographic data on the hexagonal high temperature phase of isomorph ic Cs5H3(SeO4)4.H2O.