Thermal Behaviors and Phase Evolution of Lead Zirconate Titanate Prepared by Sol-Gel Processing: The Role of the Pyrolysis Time before Calcination

Abstract

Lead zirconate titanate (PZT) (53/47) powders were fabricated by the alkoxide-based sol–gel process, and the different drying times (1 and 12 h) at the pyrolysis temperature (300°C) of lead acetate were studied. The different pyrolysis time before calcination affects the onset and the violently dominant decomposition temperatures of lead acetate. According to the estimated activation energy results, the 1 h pyrolysis time showed that the transformation of the pyrochlore to perovskite phase is nucleation-controlled (424.5 kJ/mol), but the 12 h pyrolysis time is growth-controlled (125 kJ/mol). It was also found that the relative PZT perovskite contents were controlled by the carbonaceous material contents within the dried gels and the release rate of hydrocarbon during the pyrolysis process. With the proper pyrolysis-treated PZT powders, the dense, phase-coexisted PZT bulks could be produced at a low sintering temperature of 950° and 1000°C. The phase transformation of the PZT ceramics changed from the rhombohedral phase (900°C) to rhombohedral and tetragonal phase coexistence (950° and 1000°C), then finally to the monolithic tetragonal phase (1050° and 1100°C). A phase diagram is plotted based on the different sintering conditions. The dielectric properties were dependent on the relative densities of the PZT bulks, and the PZT bulks sintered at 1000°C for 6 h had superior dielectric constant (1080) and lowest dielectric loss (0.7%).