Temperature and pressure studies of Raman peaks related to hydrogen modes in KDP

Raman scattering spectra of a KH2PO4 (KDP) single crystal have been obtained under various temperature and pressure conditions. It was observed that (i) the peak around 1310 cm−1 is not a single peak as reported previously but consists of two components and (ii) in the ferroelectric phase the 1013, 1306 and 1315 cm−1 peaks become obscure near the ferroelectric–paraelectric phase boundary. Furthermore, they show positive pressure shifts and the pressure coefficients are obtained. An interpretation is proposed for the origins of these Raman peaks.