A high pressure Raman study of KTP and pressure induced phase transitions.

Potassium titanate orthrophosphate KTiOPO sub 4 (KTP) has been studied by high pressure Raman technique to 17 GPa using a diamond cell. The Raman data reveal that two phase transitions occur in the system: one near 5.5 GPa and another near 10 GPa. The lower-pressure transition is definitely first-order but appears to be driven by the phonon mode near 56 cm sup -1, which exhibits marked softening. A mean field-like behavior is observed. It is hypothesized that this transition is likely to be from ferroelectric (FE) to an antiferroelectric (AF) phase. The 10 GPa transition may be due to AF-PE (paraelectric) transition driven by pressure from high temperature to room temperature.