Preparation of barium strontium titanate powder from citrate precursor

TiCl4 or titanium isopropoxide reacted with citric acid to form a titanyl c itrate precipitate. Barium strontium citrate solutions were then added to t he titanyl citrate reaction to form gels. These gels were dried and calcine d to (Ba,Sr)TiO3 powders. The gels and powders were characterized by DSC/TG A, IR, SEM and XRD analyses. These results showed that, at 500 degrees C, t he gels decomposed to Ba,Sr carbonate and TiO2, followed by the formation o f (Ba,Sr)TiO3. The onset of perovskite formation occurred at 600 degrees C, and was nearly complete at 1000 degrees C. Traces of SrCO3 were still pres ent. 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 re mained in solution. The titanyl citrates were precipitated in either ethano l or acetone. The acetone-derived precipitates were always viscous, but tho se 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 x 10(3), 10.2 x 10(3) and 12.5 x 10(3)m (2) kg(-1), respectively. The powder obtained by freeze-drying had the lowe st degree of agglomeration. The precipitated powders of titanyl citrate whi ch were freeze-dried and calcined at 1100 degrees C were compacted and sint ered at 1300 degrees C to obtain dense ceramic bodies with 95% of the theor etical density. Copyright (C) 1999 John Wiley & Sons, Ltd.