Longitudinal and transverse piezoelectric coefficients of lead zirconate titanate/vinylidene fluoride-trifluoroethylene composites with different polarization states

Composite films comprising lead zirconate titanate (PZT) ceramic particles dispersed in a vinylidene fluoride-trifluoroethylene copolymer matrix have been prepared by compression molding. The ceramic and copolymer phases of the composite films are polarized separately, resulting in samples with three different polarization states: only the ceramic phase polarized, both phases polarized in the same direction, and two phases polarized in opposite directions. The effect of polarization state on the longitudinal and transverse piezoelectric coefficients (d(33) and d(31)) of the composite film has been investigated as functions of ceramic volume fraction phi(c). When the ceramic and copolymer phases of a composite film are polarized in the same direction, their piezoelectric activities partially cancel each other, thereby giving almost zero piezoelectric activity at phi(c)similar to0.4. On the other hand, when the phases of a composite film are polarized in opposite directions, their piezoelectric activities reinforce. However, depolarization of the ceramic phase is observed at high phi(c), leading to a decrease in the piezoelectric activity. The observed d(33) and d(31) values for the composite films agree well with theoretical predictions. (C) 2002 American Institute of Physics.