Formation of Hexagonal Metastable Phases from an Undercooled LuFeO3 Melt in an Atmosphere with Low Oxygen Partial Pressure

Controlling the oxygen partial pressure (PO2) in the ambient atmosphere is an important parameter for material processing because the transition metal ion changes its valence depending on PO2. In the present study, containerless solidification of the LuFeO3 melt, where the undercooling level can be treated as another experimental parameter, was carried out in order to explore the unidentified metastable phases under the controlled PO2 using an aerodynamic levitator. Decreasing PO2 down to 1 × 103 Pa, the unidentified phase was solidified from the undercooled melt. The X‐ray diffractometry results after annealing at 1 × 103 Pa showed the peak profile of the stable perovskite LuFeO3 phase, suggesting that this unidentified phase was thermodynamically metastable. Thermogravimetric analysis showed that the mass of the sample solidified at PO2= 1 × 103 Pa significantly increased, suggesting that the formation of the metastable phases might be related to the presence of Fe2+ ions.