Polarization reversal and double hysteresis loop in copolymers of vinylidene fluoride and trifluoroethylene

The polarization reversal and the ferroelectric hysteresis loop have been studied for copolymers of vinylidene fluoride VDF and trifluoroethylene TrFE with 47.2, 63.0, 70.7, and 86.8 mol-% TrFE in the high voltage field up to 100 MVm⁻¹ at 5 to 100 mHz over a wide range of temperature. The copolymers exhibited two current peaks associated with the polarization process at different field intensities : one at a higher field Eh was due to the polarization reversal; the other at a lower field E1 occurred in the opposite polarity, indicating the depolarization process at high temperature. These two current peaks were related with the double hysteresis loop in the copolymers. As temperature was decreased, E1 lowered crossing zero and changed in the polarization field. The temperature at which E reduced to zero was 321, 277, 253, and 239 K for 47.2, 63.0, 70.7, and 86.8 mol-% TrFE content, respectively.