Formation of lead zirconate titanate powders by spray pyrolysis

Twin-fluid atomization spray pyrolysis (SP) has been investigated for the production of lead zirconate titanate (PZT) powders, using aqueous solutions of lead acetate and zirconium and titanium alkoxide precursor reagents. The particle size distribution of the PZT powder showed a d(50) value of 0.3 mum, but with a small fraction of relatively large particles, several micrometers in size. Most particles were spherical but many of the largest particles, in the size range ca. 1-5 mum, were irregular. It was demonstrated that the morphology of the final PZT powder was controlled by decomposition processes occurring during the initial drying stages, at less than or equal to200degreesC. A pyrochlore or fluorite-type intermediate crystalline phase was present in the final powders, but when the maximum reactor temperature was raised, and/or when the levels of excess lead in the starting solutions were increased, the proportion of the desired perovskite phase increased. However, at the highest process temperatures studied, similar to900degreesC, small crystallites of another phase formed on the surface of the PZT particles; these were probably lead oxide carbonate particles. Overall, a starting solution composition containing around 5 mol% excess Pb, and a maximum reactor temperature of 800degreesC, were selected as offering the most suitable conditions for producing PZT (52/48) powder, with minimal secondary phases(s). Preliminary densification studies showed that the powders could be sintered at 1150degrees-1200degreesC to give pellets of 95%-96% theoretical density.