Effect of Oxygen Concentration and Tantalum Addition on the Formation of High Temperature Bismuth Oxide Phase by Mechanochemical Reaction.

High-temperature face-centered cubic bismuth oxide phase is a material of great interest given its unique properties. In the present study, alpha-Bi2O3 and tantalum powders were used as the starting powders for the formation of high-temperature bismuth oxide phase via mechanochemical synthesis by high energy ball milling. (Bi2O3)(80)(Ta)(20) and (Bi2O3)(95)(Ta)(5) in weight concentrations were milled in either an oxygen-free argon-filled glove box environment or an ambient atmosphere to investigate the effects of oxygen concentration and tantalum addition. The as-milled powders were examined using X-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy, and differential scanning calorimetry to reveal the structural evolution. The experimental results showed that for (Bi2O3)(95)(Ta)(5) powder mixtures milled within the glove box, tantalum gradually reacted with the alpha-Bi2O3 phase and formed a beta-Bi7.8Ta0.2O12.2 phase. For (Bi2O3)(80)(Ta)(20) milled under the same conditions, Ta and alpha-Bi2O3 mechanochemically reacted to form delta-Bi3TaO7 and bismuth after 10 min of high energy ball milling, whereas milling (Bi2O3)(80)(Ta)(20) under the ambient atmosphere with a much higher oxygen concentration accelerated the mechanochemical reaction to less than five minutes of milling and resulted in the formation of high-temperature delta-Bi3TaO7 phase.