Hysteresis phenomena in polyvinylidene fluoride under high electric field

Abstract

Dielectric and piezoelectric responses caused by a high electric field and a 10-Hz small strain have been simultaneously measured for stretched polyvinylidene fluoride using a minicomputer system. The electric field was applied up to 240 MV/m in a sinusoidal or triangular wave form in the frequency range 10−4–10−2 Hz at temperatures between −100 and 100 °C. Ferroelectric hysteresis loops were observed even below the glass-transition temperature of −60 °C. At 20 °C the 120-MV/m electric field gave the remanent polarization Pr of 50 mC/m2 which resulted in the piezoelectric activities e31 and e32 of 70 and 7.5 mC/m2, respectively. The origin of Pr was confirmed to be the molecular dipole orientation because the value of Pr was independent of the frequency of applied field. The coercive field Ec significantly decreased with increasing temperature from 180 MV/m (−100 °C) to 25 MV/m (100 °C), while Pr showed only a slight temperature dependence.