Dielectric Constants of Crystal and Amorphous Phases in Ferroelectric Polymers

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Abstract
Dielectric constants of crystal and amorphous phases in ferroelectric copolymers of vinylidene fluoride and trifluoroethylene are separated from the dielectric constant of samples including both phases by means of a two-phase model in which the depolarization field coefficient L=1/3 is assumed. Temperature dependence of the dielectric constant of the ferroelectric crystal is not much different from that of a sample with a high degree of crystallinity, which increases during heating up to a ferroelectric-paraelectric phase transition temperature. On the other hand, the dielectric constant of the amorphous phase decreases with increasing temperature after an abrupt increase at the glass transition temperature. Although the tendency to decrease is explained as a property of liquid obeying Fröhlich-Kirkwood theory, the rate of the decrease becomes steep with increasing temperature and deviates from the theory.