Investigation of Switching Characteristics of Vinylidene Fluoride/Trifluoroethylene Copolymers in Relation to Their Structures

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Abstract
Ferroelectric switching characteristics of VDF/TrFE copolymers have been investigated over the entire range of composition for the samples subjected to drawing and/or annealing. Switching phenomena were most remarkably observed in the copolymers containing 50–80 mol% VDF. The as-cast copolymer exhibits no switching behavior because of high a depolarization field associated with low crystallinity. Draw-induced orientation of the chain axis parallel to the film surface causes an increase in the amount of reversed polarization. Annealing at a temperature between the Curie point and the melting point results in a significant increase in the degree of crystallinity and the amount of reversed polarization. Extrapolating to 100% crystallinity allows an estimation of spontaneous polarization, which is 120–135 mC/m2 for the 73/27 mol% copolymer. This value suggests a small Lorentz factor in crystals of VDF/TrFE copolymers.