Effect of Oxygen Partial Pressure on the Formation of Metastable Phases from an Undercooled YbFeO3 Melt Using an Aerodynamic Levitator

The Yb2O3–Fe2O3 system was studied to investigate the effect of oxygen partial pressure on the formation of metastable phases over a wide range of oxygen partial pressures from 105 to 10−1 Pa. Two kinds of metastable phases, with space groups of P63cm and P63/mmc, were found through rapid solidification of an undercooled YbFeO3 melt in an atmosphere with reduced Po2. The crystal structure of the as‐solidified samples changed from orthorhombic Pbnm to hexagonal P63cm and P63/mmc with decreasing Po2. X‐ray diffractometric and scanning electron microscopic results confirmed the existence of various phases in the as‐solidified samples. The stabilities of each phase were studied by annealing the bulk sample in the thermogravimetric–differential thermal analysis (TG‐DTA) furnace up to 1673 K, and the equilibrium phase diagram was constructed for the Yb–Fe–O system at 1473 K. TG analysis showed an increase of the sample mass during annealing and revealed that the existence of Fe2+, which has an ionic radius larger than that of Fe3+, decreases the tolerance factor and therefore destabilizes the perovskite structure.