フッ素系高分子強誘電体の構造と相転移

概要

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In the last few years, considerable interest has centered on the ferroelectric phenomena in fluoropolymers. An extensive review is given on the recent development of structural studies connected with ferroelectric phase transitions in polyvinylidene fluoride (PVDF) and copolymers of vinylidene fluoride/trifluoroethylene (P·VDFx/TrFE100-x) . PVDF exhibits five polymorphic forms, although the form-V is still ambiguous in its structure and properties. Various types of transitions among these forms, induced mechanically, electrically and thermally, are introduced and their mechanisms are discussed. In PVDF, the ferroelectric to paraelectric transition is not yet clearly understood. On the other hand, the Curie temperature has been recently observed in P·VDFx/ TrFE100-x. There are two kinds of phase transition from the paraelectric phase, that is, to the low temperature phase or to the cooled phase, depending on the composition x. The structures of these three crystal phases and the unique properties of the transition are introduced. The mechanisms of the phase transitions are discussed in terms of statistical theory in relation to cooperative conformational changes in the molecular chains. Finally, molecular motions in the paraelectric phase, domain structure and future problems on ferroelectric polymers are described.
日本結晶学会の論文