Effects of molar ratio of citric acid to cations and of pH value on the formation and thermal-decomposition behavior of barium titanium citrate

Several experiments were conducted to examine the effects of the molar rati o of citric acid to cations and of the pH value on the chemistry of a solut ion prepared by the Pechini method. Two types of precipitates, barium titan ium citrate (BTC) and barium citrate, developed, depending on the experimen tal conditions. Characterization of ETC by FT-IR spectroscopy and solid-sta te C-13-NMR spectroscopy indicated that barium and titanium ions were chela ted simultaneously by the central deprotonated alcoholic ligands and by dis sociated carboxylic acid groups with a unidentate type of three citric acid molecules. The possible coordinated structure of ETC was proposed. The the rmal decomposition behavior of ETC was investigated by powder X-ray diffrac tometry, FT-IR spectroscopy, and solid-state C-13-NMR spectroscopy. During decomposition, the nature of bonding between carboxylate groups and cations changed in the order unidentate --> bridging --> ionic, and carbonate spec ies were detected at 500 degrees C. A small amount of BaCO3 and the interme diate oxycarbonate coexisted at 550 degrees-600 degrees C.