Apolarizedmicro-Ramanstudyofa0.65PbMg1/3Nb2/3O3-0.35PbTiO3singlecrystal

Polarized micro-Raman spectra of a 0.65PbMg1/3Nb2/3O3-0.35PbTiO3 （0.65PMN-0.35PT） single crystal poled in the [001] direction are obtained in a wide frequency range （50-2000 cm 1） at different temperatures.The best fit to the Raman spectrum at 77 K is achieved using 17 Lorenzians to convolute into it,and this is proved to be a reasonable fit.According to the group theory and selection rules of overtone and combinational modes,apart from the seven Raman modes that are from first-order Raman scattering,the remaining ones are attributed to being from second-order Raman scattering.A comparison between the experimental results and theoretical predictions shows that they are in satisfactory agreement with each other.Our results indicate that at 77 K the sample belongs to the rhombohedral symmetry with the C 5 3v （R3m） space group （Z=1）.In our study,on heating,the 0.65PMN-0.35PT single crystal undergoes a rhombohedral → tetragonal → cubic phase transition sequence.The two phase transitions occur at 340 and 440 K,which correspond to the disappearance of the soft mode near 106 cm 1 recorded in VV polarization and the vanishing of the band around 780 cm 1 in VH polarization,respectively.