Brillouin scattering investigations of lead magnesium niobate–lead titanate single crystal

Lead magnesium niobate–lead titanate (PMN–PT) [0 0 1] single crystal of morphotropic phase boundary (MPB) composition; have been studied by 90A Brillouin scattering technique. Two phase transition anomalies were observed in the temperature dependences of Brillouin frequency shift (ν) and full-width at half-maximum of the LA and TA modes at T∼336 and ∼415 K associated with symmetry changes from R3m to P4mm and P4mm to Pm3̄m, respectively. The observed spectra showed strong polarization dependence in cubic and tetragonal phases, whereas in rhombohedral phase both the VV- and VH-scattering spectra were similar. This effect was attributed to the rotation of spontaneous polarization due to change of symmetry from P4mm to R3m.