Polarized Micro-Raman Study of the Temperature-Induced Phase Transition In0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃

Polarized Raman spectra of ferroelectric relaxor 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (0.67PMN-0.33PT) single crystal are systematically investigated in a wide temperature range from -196 to 600°C by micro-Raman scattering technique. The results clearly reveal that there are two structural phase transitions in such composite ferroelectric relaxor: the rhombohedral-tetragonal (R-T) phase transition and the tetragonal-cubic (T-C) phase transition. The former occurs at about T_R-T=34°C, corresponding to the vanishing of the soft A₁ mode at 106cm^-1 recorded in the parallel polarization. The latter appears at about T_T-C=144°C, which can be verified with the vanishing of mode at 780cm^-1 measured in the crossed polarization.