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 in 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 group 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 disordered acid hydrogen bonds and rotationally disordered water molecules on cooling. The spectroscopic results are compared with dielectric relaxation and NMR measurements on Cs5H3(SO4)4.H2O as well as with crystallographic data on the hexagonal high temperature phase of isomorphic Cs5H3(SeO4)4.H2O.