Spray pyrolysis of lead based ferroelectric materials

This work concerns the preparation of spherical, submicron, and unagglomerated lead-based ferroelectric powders by ultrasonic spray pyrolysis. Compositions investigated include: the relaxor ferroelectric lead magnesium niobate (Pb(Mg1/3Nb2/3)O3; PMN); an electrooptic composition of lanthanum doped lead zirconate titanate ((Pb1-xLax)(Zr1-yTiy)O3; PLZT); and samarium and manganese modified lead titanate (Pb1-xSmxTi0.98Mn0.02O3; PT). Spray pyrolysis as a synthesis method for producing PMN was found to be non-ideal, as fully perovskite phase powders could not be produced directly by spray pyrolysis. Preparing powders with PbO or MgO additions in excess of stoichiometry was found to improve the perovskite content of as-sprayed powders. Fully perovskite powders could be prepared by calcining powders spray pyrolyzed with 5% excess PbO at 800° C for 15 minutes. These results suggested that the short residence time in the spray pyrolysis apparatus was insufficient for the kinetically-limited growth of the perovskite phase from the cubic pyrochlore phase. Transparent PLZT was prepared by spray pyrolysis and two stage pressureless sintering. Unlike the studies on PMN, the correct stoichiometry and phase of the PLZT powders could be directly produced by spray pyrolysis. Lead titanate was prepared by spray pyrolysis, mixed oxide, and a liquid mix technique. The spray pyrolysis prepared powders exhibited an ideal morphology and agglomeration state for preparation of ceramics. The formation of oxide particles by spray pyrolysis was modeled using equations by Lang and Messing. Controlling the powder properties by manipulation of solution concentration and surface tension are discussed --Abstract, page iv