Double ferroelectric‐to‐paraelectric transition in 70/30 vinylidene fluoride‐trifluoro ethylene copolymer as revealed by dielectric spectroscopy

The variation of dielectric properties with temperature in the 1 kHz to 1 GHz frequency range for the 70/30 copolymer of vinylidene fluoride with trifluoroethylene has been associated to two processes: the β relaxation process associated with the glass transition of the amorphous phase and the ferroelectric‐to‐paraelectric crystal transition. The β process follows a Vogel‐Fülcher behavior exhibiting an anomaly in the vicinity of the crystal transition. Analysis of the ferroelectric‐to‐paraelectric Curie transition reveals the existence of a double relaxation maximum in the dielectric losses. Results have been interpreted in terms of the Havriliak‐Negami relaxation function. The variation of the relaxation strength and of the broadening parameter has been investigated as a function of temperature. The obtained results are discussed in terms of a two‐step phase transformation mechanism for the Curie transition: a first transition from the low temperature “all‐trans” ferroelectric phase to a more defective phase; a second transition from the latter phase to the final paraelectric structure.