New Brillouin spectroscopy results in CsHSeO4 between room temperature and the superionic transition

A Brillouin scattering investigation has been performed in CsHSeO4 from room temperature up to 120°C, in a temperature range where a phase transition was reported by some authors below the superionic one at 129°C. For every elastic constant under study, a slight but unambiguous change of slope is found near 50°C. The results are discussed in the light of a recent IR reflectivity study. It is concluded that the Brillouin anomalies corroborate the existence of an additional phase transition between room temperature and the superionic one.