Ultrahigh oxygen sensitivity to the formation of single-phase Bi2Ti2O7 pyrochlore during deep undercooling solidification

The effect of oxygen partial pressure ( p O 2 ) of the solidification atmosphere on the formation of single-phase Bi 2 Ti 2 O 7 prepared by deep undercooling rapid solidification was investigated. Comprehensive analyses on the solidification products showed that single-phase Bi 2 Ti 2 O 7 was highly sensitive to the presence of oxygen in the solidification atmosphere. At a low p O 2 of 1%, Bi 2 Ti 4 O 11 was identified as the secondary phase; at p O 2 of 5% and 10%, Bi 4 Ti 3 O 12 was observed as the secondary phase. The formation mechanisms of different types of secondary phases under various p O 2 were discussed from density functional theory calculations and solidification pathway analysis. Results from this work revealed the critical role of solidification atmosphere on the synthesis of single-phase Bi 2 Ti 2 O 7 by rapid solidification, and the findings might be expanded to the solidification of other metastable oxides.