Raman scattering, dielectric studies, powder and single crystal X-ray diffraction on 0.6Pb(Mg1/3Nb2/3)O3-0.4PbTiO3 (PMN-40PT) and 0.55Pb(Mg1/3Nb2/3)O3-0.45PbTiO3 (PMN-45PT) were carried out over a wide temperature range. Dielectric plots of PMN-45PT revealed two phase transitions with a sharp maximum at TC (paraelectric-ferroelectric transition at 485 K, from cubic to tetragonal with respective space groups Pm-3m and P4mm similar to PMN-40PT) and a second broad Raman shift at around 225 K. The Raman investigations confirmed the existence of phase transitions in PMN-45PT crystals, and the lowest frequency behaves like a soft mode. The appearance of diffuse scattering at room temperature in PMN-45PT suggests a phase distinct from PMN-40PT below TC. The identification of the symmetry in this temperature region will be further demonstrated.