Near-stocihoimetric barium titanate synthesis by low temperatuire hydrothermal reaction

摘要

Barium-deficiency of barium titanate particles prepared by low temperature hydrothermal reaction has been notorious. It has been believed that varium-deficiency is caused by the high solubility of barium source compared with titanium. Here is reported the synthesis of near-stoichiometric barium titanate powders with ultrafine particle size and high crystallinity by low temperature hydrothermal reaction from barium acetate and titanium tetra(methoxyethoxide). Barium titanate particles were synthesized in the spherical, metastable cubic crystalline grains with size distribution between 60 approx 90 nm in diameter. Ultrafine particle size was resulted from the control of the hydration rate and the decrease of Ti-O-Ti cross-linking extent of titanium precursor. Increasing barium to titanium molar ratio in reactant could not overcome the notorious barium-deficiency but, improved stoichometry and produced fine and less agglomerated particles. Interestingly, adding a silight pressure to autogeneous one to make total 4 approx 10 atm has yielded near-stoichiometric, higly crystalline, and less agglomerated barium titanate particles. it seems like that the total pressure around 4 approx 10 atm provides strong force enoguh to push barium ions into the interstitial poknts of perovsikte structure and stabilize it. These particles, which were in metastable cubic form as synthesized, initiated phasetransition to tetragonal form by calcination at 400 deg C.