Ferroelectric ceramics with included porosity for hydrophone applications

Porous piezoelectric ceramics have been prepared by mixing lead zirconate titanate (PZT) powder with fine particle organic additives. After mixing, the powder was cold pressed to form samples that were then heated to eliminate the organic component. Sintered samples were cut, polished, then electroded and poled in high electric field. Elastic, dielectric and piezoelectric characterisation was done on standard shape samples in agreement with IEEE standards. Important variations of those coefficients with respect to dense material were registered. In particular, the piezoelectric voltage coefficient was greatly increased. Moreover, with respect to starting dense PZT, the hydrostatic figure of merit for some compositions increased by almost two orders of magnitude, while the acoustical impedance was highly decreased. An optimum composition has been identified in order to obtain materials with high piezoelectric coefficients and reasonably good mechanical resistance and a set of samples was prepared for testing in a hydrophone device. Sensor elements with similar properties have been selected from this set and assembled in a planar hydrophone. Results on sensitivity measurements in air and under pressure are presented and discussed.