Porous PZT with tailored ultrasonic properties

For many years, PZT has been the most important piezoelectric ceramic for commercial applications. The well-known soft and hard PZT types are obtained by doping with various elements, but especially mechanical and acoustic properties cannot be altered significantly by slight modifications of the composition. However, the invention of PZT with controlled porosity has greatly extended the range of properties that can be obtained. The introduction of porosity into the structure affects all properties, and by optimising composition, porosity level and pore size it has proved possible to design materials that can replace especially lead metaniobate-based ceramics for a number of applications. The new materials combine properties normally associated with lead metaniobate, e.g. low acoustic impedance, with the well-known virtues of PZT, such as high piezoelectric coupling coefficients and the possibility to adjust the dielectric constant and the mechanical quality factor by doping. The porous PZT materials have been tested commercially and examples of specific applications are given.