Micro-Brillouin scattering study of ferroelectric relaxor Pb[(Zn1∕3Nb2∕3)0.91Ti0.09]O3 single crystals under the electric field along the [001] direction

Electric-field effects on structural phase transitions have been studied in ferroelectric relaxor Pb[(Zn1/3Nb2/3)1–xTix]O3 single crystals with x=0.09 by the high-resolution micro-Brillouin scattering. Sharp phase transitions from cubic-to-tetragonal and then from tetragonal-to-rhombohedral phases have been observed under zero-field-cooling (ZFC) condition. For two phase-transition temperatures a noticeable thermal hysteresis was clearly observed, consistent with dielectric measurements. The temperature range of a tetragonal phase has been markedly extended under the electric field of E=6.7 kV/cm along the [001] direction. A large difference of the LA-mode frequency and damping between the ZFC and field-cooling processes indicated that the multidomain structure induces the increase of the acoustic damping due to the elastic scattering. In addition, it was found that the elastic stiffness coefficient c33 in the tetragonal coordinates shows a slight decrease. The first-order character of the cubic-to-tetragonal phase transition has been gradually changed into a second-order one under the increase of the electric field along the [001] direction, reflecting a general trend of the first-order ferroelectric phase transition. Although a clear specification of the low-temperature symmetry could not be accomplished from Brillouin scattering itself, these results give new insights into an electric-field-temperature phase diagram containing phase boundaries among cubic, tetragonal, and low-temperature phases