KINETICS OF FORMATION OF THE PYROCHLORE AND PEROVSKITE PHASES IN SOL-GEL DERIVED LEAD-ZIRCONATE-TITANATE POWDER

Lead zirconate titanate (PZT) powder is prepared by the sol-gel method , The formation of pyrochlore and perovskite phases is investigated by high temperature x-ray diffraction (XRD) and thermal analysis techniq ues. The pyrochlore phase first appears in x-ray amorphous form, and t hen gets converted to crystalline state on annealing in air. We show t hat vacuum annealing of the pyrolyzed amorphous PZT gel suppresses the formation of the crystalline pyrochlore phase. This, in turn, enhance s the kinetics of conversion of pyrochlore to perovskite, such that a pyrochlore-free perovskite phase can be obtained by annealing at about 500 degrees C. On the other hand, if annealing is carried out in air, a crystalline pyrochlore phase is formed, which requires annealing te mperatures higher than 600 degrees C for transformation to the perovsk ite phase. These observations are explained tentatively in terms of th e oxygen stoichiometry of the two phases.