Piezoelectric responses in poly(vinylidene fluoride/hexafluoropropylene) copolymers

The authors show that a high transverse piezoelectric response with both high piezoelectric d(31) (d(31)=43.1 pm/V) and electromechanical coupling k(31) coefficients (k(31)=0.187), much higher than those in the piezoelectric poly(vinylidene fluoride) and poly(vinylidene fluoride-trifluoroethylene) copolymers, can be obtained in poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] 10 wt % copolymers under quasistatic condition. Furthermore, the copolymers also display a higher d(31) coefficient compared to the d(33) coefficient, which seems to be unusual compared with most other piezopolymers. The experimental data suggest that the origin of the unusual piezoelectric response in these P(VDF-HFP) copolymers originates from a reversible change between a poled alpha-like structure and beta-like structure. The phase change nature also results in a large frequency dispersion of the piezoelectric response and a smaller d(31) (=20.5 pm/V) at 50 kHz. (c) 2007 American Institute of Physics.