Dielectric study of the relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymer system

The high-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene), P(VDF-TrFE), copolymer exhibits many features resembling the relaxor ferroelectric behavior. In polymer systems, there are local dipolar motions at the monomer or unit cell scale, which manifest themselves as various relaxation processes. In this paper we investigate the relationship between the relaxor ferroelectric behavior, especially, Vogel-Fulcher (V-F) behavior and these local dipolar relaxation processes in irradiated P(VDF-TrFE) 65/35-mol% copolymer. In order to cover the change in polarization dynamics of the copolymer system, the dielectric behavior of copolymer is measured over a broad frequency (0.01 Hz-10 MHz) and temperature (−40 to 80 °C) range. The results indicate that there is an increased coupling among the local dipolar motions with reduced temperature in the crystalline region. On the other hand, the randomness introduced in the irradiation prevents the formation of a polar phase, on both the macroscale and the microscale, in the polymer. The observed relaxor behavior is a consequence of the competition of these two effects. The results further show that the V-F process of the irradiated copolymer system is different from the glass transition, which occurs in the amorphous phase of the copolymer.