Powders, fibers, thin films and aerogels: Sol-gel-derived piezoelectric materials

Sol-gel processing allows the fabrication of high quality ceramic materials as powders, films, fibers and aerogels, which by other techniques is costly, difficult or even impossible. For perowskite-phase electroceramics precise control over the stoichiometric composition of the materials and easy introduktion of donpants are additional advantages of preparation from chemical precursors. In this lecture a survey of PZT ceramics manufactured in different morphologies by sol-gel processing is presented. Precursor powders for thin films were synthesized by the reaction of zirconium- and titanium-n-propoxides with acetylacetone and lead acetate trihydrate. Coating sols can be obtained by dissolution of these powders in various solvents and solvent mixtures. PZT films with a maximum thickness of 8 um are prepared by multiple dip-coating and subsequent firing at 700°C. PZT fiberscan be attractive both for sensor and actuator applications in composite materials. Fibers are drawn in a cotinuous process directley from spinnable sol-gel precursors. After pyrolysis and sintering the fibers are embedded into polymer resins. The resulting composites were already sucessfully tested as sensor elements. In a sol-gel process utilizing an emulsion technique PZT precursor powders may be obtained for conventional ceramic processing. The final products manufactured by e.g. tape-casting and firing exhibit improved properties compared to mixed-oxide derived materials with the same composition. For ultrasonic applications in gases porous piezoelectric transducers with low acoustic impedances are required. Highly porous PZT aerogels can be prepared by sol-gel processing, supercritical drying and subsequent thermal curing. The drying conditions applied have a pronounced effect on the properties and microstructure of the final porous ceramics.