Raman spectroscopic study of structural transition in SrxBa1−xNb2O6 single crystals

c-Axis oriented single crystals of relaxor ferroelectric SrxBa1−xNb2O6 (x = 0.61 and 0.75) were investigated using polarized Raman spectroscopy and the behavior of optical phonon as a function of temperature across the phase transition from space group P4bm   to P4¯b2. Based on the polarized and depolarized spectra mode assignments were carried out. Modes of symmetry A1(LO), B1, and B2 were identified. From the detailed line shape fitting of the spectra, frequencies of the prominent modes associated with NbO6 stretching vibration were obtained. In contrast to the earlier reported results, these modes are found to exhibit discontinuous changes across the transition. The phase transition temperatures are found to be 336 and 322 K for x = 0.61 and 0.75, respectively.