Switching process in composite systems of PZT ceramics and polymers

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Abstract
The poling process in composite systems of ferroelectric PZT ceramics with a vinylidene fluoride/trifluoroethylene copolymer has been investigated by the time-domain measurements of the switching transients. The bilayer composite undergoes complete polarization reversal, although the switching time is much larger than in pure PZT. The dispersion of PZT particles in the copolymer matrix shows obscured switching transients, but polarization reversal is confirmed by reversal of piezoelectric activity. Since the dielectric constant of the copolymer is much lower than that of PZT, the applied field is greatly reduced in the PZT phase to disable instantaneous polarization reversal. However, the internal field is gradually increased with time to reach the coercive field by accumulation of real charges at the phase boundary due to the dc conductivity in the polymer phase. The conductivity also limits the switching rate to result in a long switching time. The calculated switching curve shows good agreement with observation.