Structure and ferroelectric properties of P(VDF-TrFE) copolymers

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Abstract
P(VDF-TrFE) copolymers with approximately 30 mol% of TrFE content exhibit above room temperature a ferroelectric transition of first order type with a large thermal hysteresis. We present recent investigations of the ferroelectric phase and of the phase transition using several techniques: second harmonic generation of light, high resolution X-ray diffraction, quasi-elastic neutron scattering, small angle X-ray scattering, Brillouin scattering, far infrared absorption and submillimeter dielectric spectroscopy. These results provide information on both the small crystallites and the amorphous inter-crystalline regions and show that temperature cycling throughout the Curie transition is able to modify the superstructure and to enhance the degree of crystallinity of the polymer. Accordingly, low frequency dielectric measurements, thermal expansion results and Brillouin spectroscopic investigations can be discussed in taking into account the composite structure of the semi-crystalline material.