Raman scattering study of Rb1-x(ND4)D2PO4 mixed crystal

Raman-scattering spectra of a 71.4% deuterated crystal of Rb0.52(ND4)0.48D2PO4 were studied in a wide range of temperatures down to 5 K. At low temperatures the system forms a so-called glass state, with no long range order transition to either a ferroelectric or antiferroelectric phase.We have concentrated our study on the vibrations related to the internal modes of the molecular groups (phosphate and ammonium). Special attention is focused on the v2 (symmetric deformation mode) of the PO4 and the libration mode of the ammonia, because they are very sensitive to the ordering of the protons, and to the ferroelectric- or antiferroelectric-like ordering for the former and the glass-like arrangement for the latter.