Acoustic study of ferroelectric phase transitions, from bulk materials to thin films.

The purpose of this project is to investigate how elastic properties of ferroelectric materials change when dimensionality of the specimen is reduced. Measurements done using ultrasound phase-sensitive pulse-echo technique. Ultrasound frequency ~50 MHz, length of pulses ~1us, pulse frequency ~ 10 kHz. We start investigation with bulk ferroelectric KTa_0.92Nb_0.08O₃ crystal, exploring propagation of ultrasound waves as the crystal undergoes ferroelectric transitions spontaneously and in the presence of electric field with strength from 100 V/cm up to 2 kV/cm. The speed and attenuation of sound are both sensitive to the changes in the crystal. The observed behavior can be understood in terms of a mixed model that includes elements of soft-mode and disorder to order mechanisms of the transitions. The obtained data will be applied for understanding behavior of ferroelectric films.