Ceramic–Ceramic Actuator Composed of Two Piezoelectric Layers with Opposite Poling Directions

A ceramic–ceramic actuator composed of two piezoelectric ceramic layers with opposite poling directions was developed. One layer of the actuator had a high coercive electric field (PZT (Pb(Zr,Ti)O3)-I; Ec5 1.1 kV/mm), while the other had a relatively low coercive electric field (PZT-II; Ec5 0.6 kV/mm). The actuator was fabricated by cofiring a green compact composed of the PZT-I powder on top of the PZT-II powder. When an electric field41.1 kV/mm was applied to the sintered body, the whole specimen was poled in one direction. Subsequently, by applying a field between 0.6 and 1.1 kV/mm, only the PZT-II layer was switched to the other direction. When an electric field was applied to this oppositely poled two-layer specimen, one layer of the specimen expanded while the other layer shrank. As a result of these reverse dilations, the actuator was bent into a dome shape, yielding a large axial displacement at the center. The displacement of this actuator with dimensions of 20 mm (diameter) 1 mm (thickness) was 16 lm at 0.9 kV/mm.