Effects of electrical conductivity on poling of ferroelectric composites

Composites of lead zirconate titanate ceramic particles dispersed in non-ferroelectric polymers of different electrical conductivities (polyurethane and polyethylene) have been prepared and poled under ac fields of different amplitudes Eaand frequencies f. Our experimental results reveal that the poling efficiency of the composites (as indicated by the observed remanent polarization PCR) is strongly dependent on the frequency of the poling field and the electrical conductivity of the polymer matrix. A low-frequency ac field and a high-conductivity polymer matrix would make the poling become more effective. The phenomena can be understood by the simple theoretical model, in which space charges are allowed to accumulate at the particle-matrix interfaces. The increasing trend of PCRwith decreasing f predicted by the model agrees well with the experimental results. It is suggested that the poling process is mainly governed by a crucial parameter 'relaxation time' τ of the interfacial charge. If the poling time is longer than τ, the interfacial charge can accumulate at the interfaces to stabilize the aligned dipoles in the ceramic phase, and hence the composite becomes poled. Otherwise, the composite cannot be effectively poled even under a high electric field.