PIEZOELECTRIC PROPERTIES IN THE COMPOSITE SYSTEMS OF POLYMERS AND PZT CERAMICS

Piezoelectric properties have been studied for the composite systems of PZT ceramics and polymers including polyvinylidene fluoride (PVDF), polyethylene (PE), and polyvinyl alcohol (PVA). The values of the piezoelectric constants and their temperature and frequency dependences were discussed on the basis of the theoretical expressions of the piezoelectric constants for a two-phase system with piezoelectric spherical dispersions. The piezoelectric activity of all the composite systems studied was mainly ascribed to the piezoelectricity of PZT ceramics. For the PVDF-PZT system, the piezoelectricity of PVDF was shown to make minor contribution compared to that of PZT ceramics. For the PE-PZT system, the temperature dependence of the d constant due only to elastic relaxation in the PE phase was investigated. For the PVA-PZT system, the retardational and relaxational frequency dependence of the d constant observed above 80 °C were successfully accounted for in terms of the interfacial and electrode polarizations due to the dc conduction in the PVA phase.