Effect of Temperature and Pressure on Low-Frequency Raman Scattering from Strontium Tantalate Ceramic Material

The temperature and pressure dependences of low-frequency Raman scattering were studied on structural phase transformations of Sr₂Ta₂O₇ ceramics. The Raman spectrum was measured over a temperature range from 0 to –185°C. The temperature dependence of the Raman shift of a low-lying mode of the B_1g symmetry shows at T = –110°C. This anomaly of Sr₂Ta₂O₇ is related to a ferroelectric phase transition. During cooling, the peak width of the B_1g mode shows a change at 150°C, and the temperature dependence of Raman shifts of B_3g, and B_1g modes becomes abnormal. Under high pressure, we discovered a phase transition between 4 and 5.5 GPa. Angle-dispersive X-ray diffraction data suggest the phase transition from incommensurate to commensurate states.