The dielectric, piezoelectric and hydrostatic properties of PLZT based rainbow ceramics

It has recently been shown that the selective reduction of one surface of a high-lead-containing piezoelectric or electrostrictive ceramic wafer results in a stress-biased wafer with a unique domed structure that leads to high electromechanical displacement and enhanced load-bearing capability. These ceramics have been called rainbow ceramics and their very high displacements make them very promising materials for transducers and actuators. The dielectric, piezoelectric and hydrostatic properties of a variety of PLZT based rainbow ceramics have been measured and analysed. The samples exhibited a strong piezoelectric effect in the poling direction (effective d₃₃ of the order of 10^-8 C/N) under low planar and hydrostatic pressures but as the pressure was increased there was a marked decrease in the strength of the piezoelectric response which passed through a minimum and then increased to the level of typical values for PZT ceramic. Some samples were plated and these had a low pressure hydrostatic voltage coefficient that was considerably greater than that of PZT along with a reasonable level of thickness mode electromechanical coupling. However, as the hydrostatic pressure was increased, the hydrostatic voltage coefficient decreased towards typical values for PZT. The rainbow ceramics show considerable promise as material for actuators and, possibly, for shallow water sonar transducers