Similar elastic behaviour in mhseo4 crystals near the superionic transition

Brillouin scattering investigations in NH4-, Rb- and CsHSeO4 are reported near their superionic transition. A similar elastic behaviour is observed, consisting of strong downward jumps of elastic constants C-11, C-22 and C-33, at the transition, and broadenings of the corresponding Brillouin lines above the transition. No pretransitional evolutions occur in both phases.