One-step synthesis of single-phase, bulk Bi2Ti2O7 pyrochlores by deep undercooling rapid solidification and its formation mechanism

Preparation of dense Bi 2 Ti 2 O 7 ceramics with single-phase pyrochlore structure is challenging using the conventional sintering method due to its thermal instability at ≥ 650 °C. Here we synthesized dense and phase-pure Bi 2 Ti 2 O 7 ceramics from a mixture of Bi 2 O 3 and TiO 2 by a novel deep undercooling rapid solidification method using the aerodynamic levitation technique. We reported a surprising discovery that the pyrochlore phase can exist with Bi/Ti ratio varying between 0.9 and 1.1. By a comprehensive investigation on the phase purity, crystal structure, oxidation states and electrical properties, we revealed that the pyrochlore structure is primarily stabilized by the solidification process rather than presence of a large amount of Ti 3+ . With the advantages of being containerless, one-step and fast processing, deep undercooling rapid solidification is an effective and efficient approach to prepare dense Bi 2 Ti 2 O 7 pyrochlores, and can be expanded to other thermally unstable compounds to obtain bulk materials.