Ferroelectric Phase Transitions Studied by Ultrasound Pulse-Echo

Ultrasound pulse-echo is a method of acoustic probing used to measure the physical properties of solid-state materials. Using this method, the bulk ferroelectric crystals KTa_0.92Nb_0.08O₃ (KTN) and K_0.8Li_0.2TaO₃ (KLT) are investigated as they are cooled and warmed (293-65K) through their ferroelectric phases. The KTN compound has also been investigated with an applied electric field. Measurements are performed using a highly sensitive simple homodyne phase detector, and a DC electric field that varies from 0 V/cm to >2 kV/cm. The velocity and amplitude of the ultrasound wave are both recorded against temperature to describe the properties of the crystals. The properties of the crystals being investigated are the dependence of ferroelectric phase transition temperature on an applied electric field, effects associated with the applied electric field, and possible long-term polarization of the crystal. Future work will also explore the effects of an applied electric field on KLT.