Effect of texturing conditions on the ferroelectric characteristics of vinylidene fluoride-tetrafluoroethylene copolymer films

Isomeric annealing of ferroelectric films of a vinylidene fluoride-tetrafluoroethylene copolymer uniaxially drawn at a low temperature is accompanied by noticeable enhancement of both remanent and spontaneous polarization. The analysis of optical data shows an increase in the full orientation upon annealing. As follows from spectroscopic data, the annealing leads to an increase in both crystallinity and the perfection of the crystals formed by drawing. The crystallization upon annealing proceeds via the mechanism of transition to the ordered state of amorphous-phase chains occurring in the flat zigzag conformation. A necessary condition for the aforementioned structural changes is high orientation of amorphous-phase chains in the original (before annealing) textured copolymer films. At high annealing temperatures, a decrease in orientational ordering is observed. This decrease is ascribed to the possibility of transition of ferroelectric to paraelectric crystals, which have less dense packing, at such temperatures. The occurrence of this transition is validated by shifting the Curie point to lower temperatures by a applied mechanical stress.