Structural, dielectric, and thermal investigation of the Curie transition in a tetrafluoroethylene copolymer of vinylidene fluoride

Abstract

To confirm and extend further our previous prediction of a Curie transition in PVF₂, we examined a copolymer of it with tetrafluoroethylene (81 mol % VF₂). The tetrafluoroethylene units serve to render this copolymer equivalent to PVF₂ of a slightly increased head‐to‐head content. Contrary to other reports, we have detected a Curie transition in this material using x‐ray diffraction, dielectric, and calorimetric techniques. The ferroelectric‐to‐paraelectric transformation is barely perceptible because it begins at ∼122 °C (which is only slightly below the main melting point) and is rapidly overtaken by melting. However, the reverse (paraelectric‐to‐ferroelectric) transition is detected unequivocally in the vicinity of 110–115 °C because of the metastability of the paraelectric phase that crystallizes from the melt. The dielectric peaks associated with this Curie transition are clearly separated from any contribution of bulk conduction. The characteristics of this transition are analogous to those found in copolymers of VF₂ with trifluoroethylene and thus indicate that such ferroelectric behavior is inherent to PVF₂ and does not reflect influences of any particular comonomer.