Isotopic effect in Brillouin light-scattering spectra of a Cs5H3(SO4)(4) center dot xH(2)O crystal

A Brillouin scattering study of the behavior of hypersonic longitudinal aco ustic phonons in crystalline pentacesium trihydrogen tetrasulfate Cs5H3(SO4 )(4). xH(2)O (PCHS) and its deuterated analog Cs5D3(SO4)(4). xD(2)O (DPCHS) at temperatures ranging from 420 to 120 K is reported. The effect of deute ration on the crystal lattice dynamics is investigated. The differences in the behavior of hypersonic acoustic phonons in the PCHS and DPCHS crystals suggest the existence of a hydrogen isotope effect in both the high- and lo w-temperature phases. A possible model of the isotopic effect in the high-t emperature phase is discussed. An analysis is made of the acoustic response of the PCHS and DPCHS crystals in the region of the transition to the glas slike phase. (C) 2000 MAIK "Nauka/Interperiodica".