Curie point and a space charge relaxation in ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymers with different thermal history

High-temperature processes of space charge relaxation in films of poly(vinylidene fluoride-trifluoroethylene) (70-30) have been investigated. The films were prepared by the crystallization from a solution in tetrahydrofuran at a room temperature. X-ray data analysis showed that initial films crystallize in metastable state: a paraelectric phase is formed at fast crystallization below the Curie temperature. An exothermic process was observed at heating, indicating a solid-state crystallization of metastable paraelectric regions. This process is controlled by melting of ordered regions formed at secondary crystallization. These transformations of structure affect characteristics of the high-temperature space charge relaxation process. In particular, it was found that activation energy of extrinsic conductivity is reduced by several times in the region of ferroelectric-paraelectric phase transition. An additional relaxation process was registered above the Curie temperature, which is caused by the relaxation of charges in double electric layer formed on an interface between an electrode (Au) and fluorine-containing polymer. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46186.