PHASE DEVELOPMENT IN SI MODIFIED SOL-GEL-DERIVED LEAD TITANATE

Sol-gel methods were used to prepare chemically modified lead titanate (PT) powders. A PT alkoxide solution was synthesized and doped with Si (2-12 mole %) or with equimolar amounts (2-12 mole %) of Si and Pb through the addition of Si and Pb-Si alkoxide solutions, respectively. PT alkoxide solutions were also prepared with excess Pb and Ti (7 and 10 mole %). Gels were prepared through controlled additions of water. Crystalline phase development of gel-derived powders with heat treatment (400-700-degrees-C) was studied using x-ray diffraction (XRD) and differential thermal analysis (DTA). While PT powders without added Si crystallized directly into a perovskite phase, Si modified materials crystallized first into a pyrochlore phase and at a higher temperature transformed into perovskite. The pyrochlore lattice parameter and the temperature for the transformation to perovskite increased with Si content. In all cases, the crystal structure of the final perovskite phase was not affected by the Si addition. The effect of Si on phase development and mechanisms of transformation is discussed.