Field dependence of polarization in poly(vinylidene fluoride) derived from quasi-stationary poling currents

摘要

In recent studies,1,2 switching characteristics of PVDF were investigated in the time domain by measuring charge and current responses to the stepwise application of electric fields in circuits with RC time constants smaller than 1 µS. Switching times for polarization reversal of 4 µS and larger were reported depending on the field strength and temperature.1,2 Similar shapes of current vs. time curves were found in circuits with RC time constants longer than the above reported switching times and these results were also interpreted as being the characteristic switching times of the polymer dipoles.3,4 More recently, we measured the poling current and the piezoelectric stress coefficient e31 as functions of poling time in circuits with RC values ranging between 0.1 and 1000s.5 We found that the time between the voltage application and the occurrence of polarization current maximum was proportional to the value of RC. Furthermore, the temporal buildup of the e31 coefficient also scaled with the time constant. In addition to these studies, similar results were observed in hysteresis measurements at low cycling frequencies where the hysteresis loop of electrical displacement versus field strength was found to be independent of frequency.6 These results suggest that it is possible to perform experiments in the quasi steady state where the time dependence of switching is not important.