Piezoelectric PZT / PVDF-copolymer 0-3 composites: aspects on film preparation and electrical poling

Composite films of lead zirconate titanate (PZT) and different (non-polar and polar) polyvinylidene fluoride (PVDF) copolymers are prepared as 30 to 150 μm thick freestanding, relatively flexible films. For low ceramic-volume fractions the ceramic fillers are homogeneous distributed within the polymer matrix as indicated by scanning electron microscopy studies. Ceramic-volume fractions higher than approximately 0.5 lead to porous composite films which became brittle. The brittle films are difficult to polarize and not suitable as piezoelectric transducers. The permittivities of non-porous composite films follow the Bruggeman model for dielectric mixtures. Different procedures are presented and verified in order to polarize the ferroelectric PZT particles and the ferroelectric polymer matrix. In detail, the overall polarization is discussed by taking into account the polarities of the applied poling voltage and of the measured piezoelectric signals. In summary, for composites with high ceramic-volume fractions piezoelectric coefficients of up to 8.6 pC/N and 22.1 pC/N (for PZT / P(VDFTrFE) composites) and up to 11.3 pC/N and 24.8 pC/N (for PZT / P(VDF-HFP) composites) are reached after short-term, room-temperature and long-term, high-temperature poling, respectively.