The dependence of the piezoelectric response of poly(vinylidene fluoride) on phase-I volume fraction

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Abstract
Investigations of the dynamic piezoelectric response (d*31 and e*31) of unoriented poled poly(vinylidene fluoride) films containing different volume fractions of phase‐I and phase‐II crystalline materials show a linear relationship between phase‐I content and piezoelectric response. Samples were poled under conditions (106 V/cm at 23 °C) which produced no observable changes in x‐ray diffraction patterns taken before and after poling. The piezoelectric strain constant of the unoriented phase‐II film is d′31=0.48×10−12 C/N, while that of the unoriented phase‐I sample is d′31 =6.68×10−12 C/N. The data supports a model in which the piezoelectric activity is primarily due to a bulk polarization of the PVF2 by a 180° dipole switching mechanism in the polar phase‐I crystals.