The Dependence of Dielectric and Ferroelectric Properties on Crystal Phase Structures of the Hydrogenized P(VDF-TrFE) Films With Different Thermal Processing

Different thermal treatments were used to obtain various crystal structures of hydrogenated poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] films synthesized by an atom transfer radical chain transfer and controllable elimination reaction route. After analyzing the results of X-ray diffraction and differential scanning calorimeter, we found that these P(VDF-TrFE) samples possessed mixed crystal phases of alpha, beta, and gamma with various compositions depending on the TrFE content and processing temperature, and this characteristic was also demonstrated by the dielectric temperature curves. After polarizing the P(VDF-TrFE) samples at different electric fields, the effect of crystal structure on their ferroelectric and piezoelectric properties was illustrated and conformed by field emission scanning electronic microscopy morphology, which was found that large TrFE content and high temperature processing were responsible for the large remnant polarization. As a result, the annealed P(VDF-TrFE) 80/20 mol% possessed a high remnant polarization of 9.2 mu C/cm(2), a large piezoelectric value (d(33) = -25 pC/N), and a favorable electromechanical coupling factor (k(t) = 0.26), providing a reliable method for the structure design and sample fabrication of this kind of copolymer aimed at the applications in piezoelectric sensors and actuators.