Synthesis of Ba2Ti9O20 materials via a dissolution-precipitation mechanism in a hydrothermal process

A hydrothermal process has been successfully utilized for the preparation of Hollandite-like Ba2Ti9O20 precursors. Transmission electron microscopy in conjunction with chemical analyses of reacted powders indicate that Ti4+ species are first dissolved in the solution and then react with Ba2+ species to form perovskite-phased BaTiO3 in the hydrothermal process. An excessively large particle size for the starting TiO2 (anatase powders) results in insufficient Ti ions in the solvent and incomplete reaction with Ba2+ species, which leads to a Ba2+ -deficient powder mixture. A residual TiO2 phase thus results after calcination. Only small TiO2 particles (40 nm) can result in sufficient Ti4+ species in the solution, which fully react with Ba2+ species and lead to a TiO2/BaTiO3 ratio of the correct stoichiometry to form Ba2Ti9O20. TiO2/BaTiO3 powder mixtures prepared in this way possess high activity and can be converted into pure Ba2Ti9O20 materials. After calcination and sintering processes, such materials possess high sintered density (similar to 93% TD) and good microwave dielectric properties (K = 36 and Q x f= 27,000). (c) 2005 Acta Materialia, Inc. Published by Elsevier Ltd. All rights reserved.