Solution based synthesis of perovskite-type oxide films and powders

摘要

Conventional solid state reactions are diffusion limited processes that require high temperatures and long reaction times to reach completion. In this work, several solution based methods were utilized to circumvent this diffusion limited reaction and achieve product formation at lower temperatures. The solution methods studied all have the common goal of trapping the homogeneity inherent in a solution and transferring this homogeneity to the solid state, thereby creating a solid atomic mixture of reactants. These atomic mixtures can yield solid state products through diffusionless mechanisms. The effectiveness of atomic mixtures in solid state synthesis was tested on three classes of materials, varying in complexity. A procedure was invented for obtaining the highly water soluble salt, titanyl nitrate, TiO(NO(sub 3))(sub 2), in crystalline form, which allowed the production of titanate materials by freeze drying. The freeze drying procedures yielded phase pure, nanocrystalline BaTiO(sub 3) and the complete SYNROC-B phase assemblage after ten minute heat treatments at 600 C and 1,100 C, respectively. Two novel methods were developed for the solution based synthesis of Ba(sub 2)YCu(sub 3)O(sub 7(minus)x) and Bi(sub 2)Sr(sub 2)Ca(sub 2)Cu(sub 3)O(sub 10). Thin and thick films of Ba(sub 2)YCu(sub 3)O(sub 7(minus)x) and Bi(sub 2)Sr(sub 2)Ca(sub 2)Cu(sub 3)O(sub 10) were synthesized by an atmospheric pressure, chemical vapor deposition technique. Liquid ammonia solutions of metal nitrates were atomized with a stream of N(sub 2)O and ignited with a hydrogen/oxygen torch. The resulting flame was used to coat a substrate with superconducting material. Bulk powders of Ba(sub 2)YCu(sub 3)O(sub 7(minus)x) and Bi(sub 2)Sr(sub 2)Ca(sub 2)Cu(sub 3)O(sub 10) were synthesized through a novel acetate glass method. The materials prepared were characterized by XRD, TEM, SEM, TGA, DTA, magnetic susceptibility and electrical resistivity measurements.