Structure and Properties of Ferroelectric Polymers

Abstract

Copolymers of vinylidene fluoride with trifluoroethylene have been shown to be a ferroelectric polymer undergoing polarization reversal and the Curie transition. Besides ferroelectricity, they have an interesting character that annealing at a temperature in the paraelectric phase causes a remarkable increase in crystallinity as well as a growth of large crystalline lamellae. We have prepared the copolymer samples with well-defined higher order structures and examined their properties such as ferroelectric switching, non-linear dielectricity, piezoelectricity and pyroelectricity. For example, the samples annealed at just below the melting point are found to consist of crystallites thicker than 200nm and exhibit very sharp ferroelectric switching transients while those annealed at lower temperatures exhibit no or extremely broad switching transients. On the basis of these results, the microscopic mechanisms responsible for their ferroelectricity will be discussed.