Direct piezoelectric response of piezopolymer polyvinylidene fluoride under high mechanical strain and stress

We show that the nonlinear piezoelectric response of polyvinylidene fluoride (PVDF) exhibits quite different behavior compared with the piezoceramics. Instead of increasing linearly with the stress amplitude Tac, d31 coefficient raises with Tac2. Furthermore, the nonlinear effect does not set in until the strain increases beyond 0.3%, indicating very strong barriers to the domain wall motions in PVDF. The electromechanical coupling factor k31 also exhibits an increase with stress. Furthermore, the piezopolymer can withstand more than 3% strain without degrading the piezoelectric responses.