The transition to a proton glass state in Cs 5H 3(SO 4) 4 · H 2O

Abstract

Raman scattering, calorimetric and dielectric spectroscopy data for Cs 5H 3(SO 4) 4 · H 2O single crystals taken at 20–300 K are reported. The glass transition temperature, T g, as determined from DSC, shows a remarkable hysteresis: 261 K on heating and 248 K on cooling. The change in the molar heat capacity is 27 J/mol · K. The dielectric data (30 kHz–2.2 MHz) show a pronounced dispersion whose relaxation frequency obeys an Arrhenius law. An increase in the Isotropie component of Rayleigh light scattering was observed below T g. Raman scattering data indicate a conservation of hexagonal crystal symmetry in the glassy phase, and a lowering of the site symmetry. The transition from dynamic to static disorder is discussed.