A self-sustaining acid-base reaction in semi-aqueous media for synthesis of barium titanyl oxalate leading to BaTiO3 powders

A self-sustaining controlled acid–base reaction between oxalotitanic acid [H2TiO(C2O4)2] (HTO) and barium hydroxide [Ba(OH)2� 8H2O] at room temperature is utilized for the quantitative precipitation of barium titanyl oxalate (BTO). For this purpose, an intermediate soluble oxalotitanic acid precursor is generated by reacting 0.1 M solution of titanium tetrabutoxide in isopropanol (IPA) with 0.2 M solution of oxalic acid in IPA. Equimolar suspended Ba(OH)2 particles in IPAwere mixed with the above-mentioned oxalotitanic acid solution. The self-sustaining acid–base reaction between Ba(OH)2 and H2TiO(C2O4)2 was initiated only when necessary amount of water was added. This shift from non-aqueous to semi-aqueous condition allows a required solubility of Ba(OH)2, which makes Ba 2+ ions available for the exchange reaction. The solubility of Ba(OH)2 and its dissociation governs the kinetics of the reaction leading to the precipitation of BTO with yield z99%. The controlled pyrolysis of BTO at 750 jC/4 h in air-produced agglomerated cubic BaTiO3 powders having spherical particles with size c100 nm. These powders are sintered in the form of pellets at 1300 jC/4 h to obtain compacts with density c95%. These compacts showed dielectric constant eRT=1680 (tandV2%), emaxc7780 at TC=121 jC. D 2002 Elsevier Science B.V. All rights reserved.