Temperature-dependent Raman spectra and electrical properties of 0.69Pb(Mg1/3Nb2/3)O3-0.31PbTiO3 single crystals

The temperature-dependent Raman spectra and electrical properties of the 0.69Pb(Mg1/3Nb2/3)O-3-0.31PbTiO(3) (0.69PMN-0.31PT) single crystals were investigated. Based on the group theory, the poled 0.69PMN-0.31PT single crystals belong to the monoclinic crystal system, which was confirmed by the room-temperature Raman spectra. The 0.69PMN-0.31PT single crystals experience successive structural phase transitions, i.e., a monoclinic-tetragonal (FEM-FET) phase transition at TM-T and a tetragonal-cubic (FET-P-C) phase transition at T-m determined by the dielectric measurement. Due to the enhancement of long-range order, their FEM-FET phase transition becomes more obvious after the poling process. The wavenumbers and line widths of the 271, 502, 575, 795 cm(-1) Raman modes, and the intensity ratios of I271cm-1/I795cm-1 and I502cm-1/I575cm-1 exhibit obvious anomalies around TM-T and T-m, which are closely related to the FEM-FET and FET-P-C phase transitions. The temperature and electric field (E)-induced phase transitions are observed in the unipolar strain-E (S-E) curves. The converse piezoelectric constant (d(33)), maximum strain value (S-max%) and longitudinal electrostrictive coefficient (Q) increase considerably around the ferroelectric phase transition temperature T-M-T(.)