Synthesis of Polytitanates from $Ba(OH)_2-TiO_2-H_20$ System through Gel to Crystallite Conversion

Some of the compounds in the $BaO-TiO_2$ system exhibit good dielectric properties at microwave frequencies. They find importance as dielectric resonators in microwave integrated circuits and in microwave filters. $BaTi_40_9$ and $Ba_2Ti_90_{20}$ are titania-rich compounds that are of considerable interest for microwave dielectric applications. The dielectric constant of these materials is higher (38 to 40 at 10 GHz) than most other materials in the microwave region, which allows miniaturization of the resonance circuits without decreasing the Q-values. Polytitanates of barium are mostly prepared by the high temperature reaction of the constituefit oxides at appropriate $BaO:TiO_2$ ratios. The subsolidus phase relations in the system $BaTiO_3-TiO_2$ have been studied by Statton and Rase and Roy, while the phase equilibrium in the $TiO_2$-rich part of the system has been invéstigated by Negas et al. and by O'Bryan and Thomson. Suwa et al. and Ritter et al. have attempted the low-temperature alkoxide precursor routes for the preparation of various polytitanate phases. Kutty and Murugaraj have synthesized polytitanates through hydrothermal preparations. They reported the stabilization of $Ba_2Ti_{5.5}O_{13}$ using the hydrothermal route in stainless steel autoclaves. They have attributed this phenomenon to the effect of impurities from the stainless steel autoclaves. Tillmanns et al. have systematized the crystal structure relations in barium polytitanates