Nano-sized barium titanate powders with tetragonal crystal structure prepared by flame spray pyrolysis

Nano-sized BaTiO₃ powders with regular morphology and tetragonal crystal structure were prepared by flame spray pyrolysis from a spray solution with citric acid. The precursor powders prepared at the low flow rates of fuel gas at 2 and 2.5 L/min had large, hollow, thin wall structures. On the other hand, the precursor powders prepared at a high flow rate of fuel gas at 4 L/min had a dense submicronic structure. Those precursor powders with a hollow, thin wall structure formed a slightly aggregated BaTiO₃ of nanometer-sized primary powders after post-treatment. The slightly aggregated BaTiO₃ became nano-sized powders via a simple milling process. The mean sizes of the powders changed from several tens to 200 nm when post-treatment temperatures changed from 700 to 1000 °C. The BaTiO₃ powders obtained from the citric acid spray solution had tetragonal crystal structure at post-treatment temperature of 1000 °C. Conversely, those BaTiO₃ powders prepared from a spray solution that did not contain citric acid had cubic crystal structures at this same post-treatment temperature.