Solid Phase Nucleation of Lead-Based Perovskites and their Properties

This is the renewal of research on the principles and application of controlled nucleation during alpha aluminum oxide phase transformation. It was established that by controlling the nucleation of the reaction through the addition of crystallographically similar substrates (i.e., seeds) upon which the reaction is initiated epitaxially, the nucleation barrier to reaction is almost eliminated, the incubation period for reaction is significantly reduced, the reaction time and temperature are reduced, and the particle size is reduced. The current grant includes the study of these principles on lead-based perovskites, lead magnesium niobate and lead zinc niobate. The studies focus on the epitaxial relations between the seed crystal and mixed metal oxide precursor, growth of the nucleated perovskite as a function of transport path, microstructural evolution and electrical properties. Polymeric sols will be used to study epitaxial relations as a function of lattice mismatch and transport path. Seeded sols will be used to determine transformation kinetics, microstructural evolution and for preparation of specimens for evaluation of electrical properties. The materials being investigated are used in the electronic industry for dielectrics. They are difficult to synthesize with reproducible properties. The research under this grant is relevant to new processing techniques which lower the processing temperature, and potentially improve control of the structure. Training of students with experience to perform research on these technologically important materials is a significant component of the grant.