The effect of crystallinity on observed polarization hysteresis loops in polyvinylidene fluoride

It is demonstrated experimentally that electric fields cause conversion of α to β crystals and a growth of β crystals in PVDF (polyvinylidene fluoride). The former process leads to an increase in sample polarization as measured by external circuitry. Since β crystals are polar and α crystals are not, this increased polarization is to be expected. The field-induced growth of β crystals appears to lead to a decrease in sample polarization, but the cause for this is not so readily apparent. A detailed model for polarization reversal in ferroelectric polymers, which includes the contribution of the depolarizing field within the crystals, predicts that the length-to-width ratio of the crystals will have an effect on the observed hysteresis loops. Thus, a possible explanation of the reduction in macroscopic polarization is that the field-induced growth of β crystals alters the length-to-width ratio of the lamellar crystals, thus reducing the depolarizing field within the crystal