Pressure Driven Structural Evolutions of 0.935(Na_0.5Bi_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(Na_0.5Bi_0.5)TiO_3-0.065BaTiO_3 (NBT-6.5BT) is systematically investigated via in situ Raman spectroscopy. The pressure dependence of phonon modes up to 30 GPa reveals two characteristic pressures: one is at around 4.6 GPa 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 \sim 13–15 GPa with certain degree of order-disorder transition, evidenced by the abnormal changes of intensity and FWHM in Raman spectrum.