Temperature dependence of the Raman spectra of RbH2PO4 and RbD2PO4

Raman spectra in the ferroelectric and paraelectric phases of RbH2PO4 (RDP) and RbD2PO4 (DROP) ferroelectric crystals have been measured. The internal modes of the PO43- tetrahedra indicate that its symmetry in the paraelectric phase is S4 as a temporal average of two ferroelectric configurations of C2 symmetry.These results indicate, as in KDP, that the phase transition mechanism can be related to the order-disorder dynamics of PO34 tetrahedra, instead of the usual proton tunneling process.