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

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Abstract
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.

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