Structure and Spontaneous Polarization in Fast-Quenched Copolymers of Vinylidene Fluoride and Trifluoroethylene

Fast quenching from the melt was found to effect greatly the structures and ferroelectric properties of vinylidene fluoride and trifluoroethylene copolymers (P(VDF/TrFE) in contrast to slow cooling. The results are discussed for high- and low-VDF content divided at about 50 mol% VDF. For the high-VDF copolymers, the quenched samples showed high Tc like poled samples, implying an ordered ferroelectric phase. Poling the quenched samples at elevated temperatures produced a ferroelectric polarization the direction of which was restored after cooling from above Tc. For the low-VDF copolymers, the quenched samples showed a crystalline phase different from that of the slow-cooled samples, which was found to exist in a metastable state. The quenched samples exhibited no ferroelectricity unlike the slow-cooled samples but poling at elevated temperatures induced pyroelectricity with anomalous temperature dependence. From the present results, the fast quenching seems to produce a phase stable at low temperatures and the poling at elevated temperatures causes crystal growth under an electric field resulting in thermally-stable spontaneous polarizations. Crystal structures of the low-VDF copolymers are also speculated based on the present results and published structure models.