Preparation of barium strontium titanate powder from citrate precursor

Abstract

TiCl 4 or titanium isopropoxide reacted with citric acid to form a titanyl citrate precipitate. Barium strontium citrate solutions were then added to the titanyl citrate reaction to form gels. These gels were dried and calcined to (Ba,Sr)TiO 3 powders. The gels and powders were characterized by DSC/TGA, IR, SEM and XRD analyses. These results showed that, at 500 °C, the gels decomposed to Ba,Sr carbonate and TiO 2 , followed by the formation of (Ba,Sr)TiO 3 . The onset of perovskite formation occurred at 600 °C, and was nearly complete at 1000 °C. Traces of SrCO 3 were still present. The cation ratios of the titanate powder prepared in the pH range 5–6 were closest to the original stoichiometry. Only 0.1 mol% of the free cations remained in solution. The titanyl citrates were precipitated in either ethanol or acetone. The acetone-derived precipitates were always viscous, but those with a sufficient quantity of alcohol were powdery. The specific surface areas of the ceramic powders obtained by air- , vacuum- and freeze-drying methods were 8.3 14× 1410 3 , 10.2 14× 1410 3 and 12.5 14× 1410 3 m 2 kg −1 , respectively. The powder obtained by freeze-drying had the lowest degree of agglomeration. The precipitated powders of titanyl citrate which were freeze-dried and calcined at 1100 °C were compacted and sintered at 1300 °C to obtain dense ceramic bodies with 95% of the theoretical density. Copyright © 1999 John Wiley & Sons, Ltd.