DEPENDENCE OF THE PIEZOELECTRIC RESPONSE OF POLY(VINYLIDENE FLUORIDE) ON PHASE-I VOLUME FRACTION

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.