Acoustic and Dielectric Loss Processes in PVF2

Abstract

Acoustic and dielectric properties of homemade and commercial piezoelectric PFV2 have been measured for samples with thicknesses between 26 and 260 pm using the acoustic resonator method. The influence of temperature from - 40 to 90' C has been investigated for frequencies between 2 and 50 MHz. The dielectric and acoustic loss processes are discussed. Different phase transitions have been shown up by observing the behavior of the dielectric loss factor versus temperature. At room temperature the acoustic loss is a linear function of frequency. Then the conventional phonon-phonon coupling losses are negligible. The frequency independent term of acoustic losses has been attributed to a macromolecular chain relaxation tail with a relaxation frequency smaller than the operating frequencies at room temperature. Results obtained by the thermostimulated measurement technique in which no driving voltage nor strain is used do not exhibit such a linear frequency dependence of losses. It is concluded that the periodic driving voltage applied to the resonators involves a hysteresis-type process in the macromolecular chain motion.