Corroboration of an intermediate phase transition in CsH2PO4 by Brillouin spectroscopy between room temperature and the superionic phase transition

An investigation of elastic properties of CsH2PO4 by Brillouin spectroscopy has been performed between room temperature and the superionic transition, which takes place near 230°C. For every elastic constant under study a slight but unambiguous change of slope is found around 120°C. The results are discussed in the light of other experimental ones, in particular those related to sample dehydration which could suggest the absence of any phase transition above room temperature, as recently claimed. It is concluded that the Brillouin results corroborate the existence of a polymorphic transition near 120°C.