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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 Pm&3macr;m, 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. [Copyright &y& Elsevier]