Preparation of SrBi₂Ta₂O₉ from metal alkoxides

SrBi₂Ta₂O₉ (SBT) has potential application in FERAM. Some problems in the sol-gel processing of SBT, such as the solubility of metal alkoxides, chemical modification with a chelating reagent and crystallization behavior of the gels, are investigated. The starting solutions were prepared with Sr(OC₄H₉)₂, Bi(OC₃H₇)₃, and Ta(OC₂H₅)₅. Ethoxyethanol and acetylacetone (ACAC) were used as solvent and chelating reagent, respectively. Ta- and Bi-alkoxide are chemically modified with ACAC, but Sr-alkoxide was not. The SBT solution was stabilized with ACAC for ca. 3 months. After hydrolysis of the SBT solution with the addition of ACAC, a monolithic and transparent gel was obtained at room temperature in 100 days. The X-ray diffraction peaks of SBT and very weak peaks of SrTa₂O₆ (ST) and SrBi₂O₄ (SB) were found after calcination at 700°C for both of the gels obtained with and without addition of ACAC. In contrast, the stronger peaks of ST and SB were observed for the powder mixture of SrCO₃, Bi₂O₃, and Ta₂O₅ after calcination at 800°C. These results show the better homogeneity of the gels.