Application of a second order response theory to the nonlinear piezoelectricity of PVDF

The piezoelectric response of poly(vinylidene fluoride) is known to be a nonlinear function of stress. A second-order response theory is applied to this phenomenon. The derived equations allow the determination of nonlinear coefficients from the linear part of the response after a static stress is applied. Experimental results indicate that two molecular processes contribute to the macroscopic piezoelectricity, differing in the sign of their polarization. The contribution of each process depends on the static stress and the frequency