Rhombohedral-to-tetragonal phase transformation and thermal depolarization in relaxor-based ferroelectric single crystal

摘要

The rhombohedral-to-tetragonal (R-T) transformation in relaxor single crystals occurs over a temperature range, manifested by the coexistence of rhombohedral ? and tetragonal (T) microscopic and nanotwin domains, a string of thermal current signals, and continued degradation of dielectric and electromechanical properties. Thermal current and high-resolution x-ray diffraction results suggest T_(RT)≌ 100-135 ℃ for [001]-poled PZN-4.5%PT and 90-115 ℃ for [001]-poled PZN-7%PT. The "T_(RT)" determined from the dielectric permittivity-temperature plot of poled crystals corresponds to the lower bound of T_(RT), which is also a good indication of the depolarization temperature (T_(DP)) of relaxor ferroelectric single crystals above which perceptible property degradation begins.