Abnormal phase transitions for tetragonal (1-x)Pb(Mg[sub ⅓]Nb[sub ⅔])O₃-xPbTiO₃ single crystals at low temperature

Abstract

Dielectric spectroscopy and ultrasonic sound velocity were investigated for tetragonal PMN-xPT single crystals over a wide range of temperature. In addition to the expected phase transition from the tetragonal ferroelectric phase to the cubic paraelectric phase at a high temperature, an abnormal ferroelectric phase transition below room temperature is observed. The low-temperature phase transition shows a relaxor behavior though tetragonal PMN-xPT single crystal is considered to be typical normal ferroelectrics. By comparing the dielectric constants of poled and depoled conditions and by analyzing [BO[sub 6]] oxygen-octahedra units of perovskite structure, it is suggested that the low-temperature phase transition in poled tetragonal PMN-xPT single crystal could be tetragonal to rhombohedral ferroelectric phase transition.