Pressure Driven Structural Evolutions of 0.935(Na_(0.5)Bi_(0.5))TiO_3-0.065BaTiO_3 Lead-Free Ferroelectric Single Crystal through Raman Spectroscopy

Pressure evolution of local structure and vibrational dynamics of the perovskite-type relaxor ferroelectric single crystal of 0.935(Na0.5Bi0.5)TiO3-0.065BaTiO3(NBT-6.5BT)is systematically investigated via in situ Raman spectroscopy.The pressure dependence of phonon modes up to 30GPa reveals two characteristic pressures:one is at around 4.6GPa which corresponds to the rhombohedral-to-tetragonal phase transition,showing that the pressure strongly suppresses the coupling between the off-centered A-and B-site cations;the other structural transition involving the oxygen octahedral tilt and vibration occurs at pressure～13–15GPa with certain degree of order-disorder transition,evidenced by the abnormal changes of intensity and FWHM in Raman spectrum.