Effects of porosity and grain sizes on the dielectric and piezoelectric properties of porous PZT ceramics and their mechanism

Porous lead zirconate titanate (PZT) ceramics were prepared by adding pore formers, and the effects of pore structure and grain sizes on the dielectric and piezoelectric properties of samples were investigated. The research showed that an increase in the porosity led to reduced dielectric constant as well as enhanced hydrostatic figures of merit (dh·gh). The effect of porosity on dielectric constant can be predicted by the Okazaki experiential formula and Banno model under certain conditions. An increase in grain size increases the dielectric constant, piezoelectric coefficient and hydrostatic figures of merit, which can be explained by the Okazaki space-charge theory. For the sample with 10 wt% PMMA additions sintered at 1300℃, the porosity is 34% and the longitudinal piezoelectric coefficient (d33) is very close to that of dense PZT ceramics, while the hydrostatic figures of merit (dh·gh) is about fifteen times greater than that of dense PZT ceramics. Compared with PZT-polymer composites, the dielectric constant and piezoelectric coefficient of 34% porous PZT sintered at 1300℃ is much higher and can be more efficient in resisting the interference from the ambient medium.