Ferroelectric order and phase transition in polytrifluoroethylene

Polarization‐reversal currents and x‐ray profiles under a high dc field were measured on polytrifluoroethylene (PTrFE) samples prepared by melt crystallization at different cooling rates. The results for PTrFE were found to be analogous to those for copolymers of vinylidene fluoride and trifluoroethylene [P(VDF/TrFE)] with low VDF content. Slow‐cooled and quenched samples showed different x‐ray profiles but the same IR spectra. For the slow‐cooled samples, a polarization reversal was clearly observed as a peak in polarization current, offering evidence for ferroelectric order in PTrFE. The ferroelectric behavior was found to be unlike that of typical ferroelectric polymers. There are two processes in a polarization reversal, i.e., partial depolarization reversal, accompanied by crystalline phase transitions. It is noted that no ferroelectric order was observed for the quenched sample which, however, becomes pyroelectric by poling as revealed by our previous studies. We speculate on possible crystal structures of PTrFE based on the published structure models and the present results. The relation between the ferroelectricity and the previously reported pyroelectricity is also discussed.