Dielectric relaxation behavior and its relation to microstructure in relaxor ferroelectric polymers: High-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) copolymers

The dielectric behavior of the high-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) 68/32 mol % copolymer was characterized in the dose range from 0 to 175 Mrad. It was found that as the dose increases, the copolymer evolves from a normal ferroelectric to a relaxor ferroelectric and then to a simple relaxor. Correspondingly, the crystalline morphology changes from a two-phase coexistence between a polar and nonpolar phases at low doses (<50 Mrad) to a macroscopically uniform nonpolar phase for doses beyond 50 Mrad, as revealed by x-ray data. Interestingly, it was observed that in the whole dose range, the Vogel-Fulcher (V-F) relationship could describe the measured relationship between the frequency and the peak temperature of dielectric constant well. For the copolymers irradiated with dose near 75 Mrad, which show a typical relaxor ferroelectric response, the V-F behavior is a result of freezing of the relaxation time (into polar glass state). For the copolymers irradiated with doses lower that 50 Mrad where a polar phase and nonpolar phase coexist, the dielectric data at near the ferroelectric-paraelectric temperature show a dielectric peak with V-F type relaxation followed by a transition from a relaxor ferroelectric and normal ferroelectric as the temperature is lowered, suggesting a possible freezing process even in this dose range. (C) 2002 American Institute of Physics.