Influence of composition on relaxor ferroelectric and electromechanical properties of poly(vinylidene fluoride-trifluoroethylene- chlorofluoroethylene)

We investigate the influence of the composition, especially the chlorofluoroethylene content, on the ferroelectric and electromechanical properties of the poly(vinylidene fluoride-trifluoroethylene- chlorofluoroethylene) (PVDF-TrFE-CFE). It was found that increasing the CFE from $0\text{to}9\mathrm{mol}\%$ gradually converts the normal ferroelectric of the copolymer (in the compositions range of VDF/TrFE mole ratio between $64∕36$ to $75∕25$ ) to a relaxor ferroelectric, resulting in a nearly hysteresis free polarization loop and high electrostrictive response. On the other hand, increasing CFE content causes reduction in crystallinity, which will affect the elastic modulus and the induced polarization level of the polymer. These competing effects determine the desired terpolymer compositions for given applications. The electromechanical strain as a function of induced polarization and macropolar phase fraction was modeled by a modified electrostrictive relation, which closely matches experimental data. It is found that the electrostrictive coefficient is relatively constant across the compositions investigated.