Effect of space charge on polarization reversal in a copolymer of vinylidene fluoride and trifluoroethylene

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Abstract
Polarization-reversal phenomena in ferroelectric copolymers of vinylidene fluoride and trifluoroethylene are affected by the time interval elapsed after poling of samples. Measurements of switching current demonstrated that this waiting effect is enhanced with the increase of space charges and switching curves with different waiting intervals satisfy the scaling rule when each switching curve is scaled by the switching time. These facts suggest that the electric field that reverses the spontaneous polarization decreases due to the electric field coming from space charges in the amorphous phase. A model with a prolate ellipsoid crystal and space charges in the amorphous phase explains such experimental facts. The difference of the waiting effect among samples crystallized under different conditions is also explained through the difference in the depolarization field coefficient of crystals.