Using containerless processing with an aerodynamic levitation furnace, LaO3/2–TiO2 binary glasses were synthesized in bulk form. Glass‐forming region was found in the vicinity of eutectic point, which is approximately 29.5% LaO3/2 and 70.5% TiO2 in molar ratio. The glass transition temperature Tg and the crystallization onset temperature Tx of the obtained glasses were determined by differential scanning calorimetry. The thermal stability was evaluated by ΔT (=Tx − Tg). Our experimental results were compared with phase diagram of the LaO3/2–TiO2 binary system. Glass compositions with highest ΔT corresponded to single‐phase compound of La4Ti9O24 and the eutectic point.

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.

The Yb 2 O 3 -Fe 2 O 3 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 10 5 to 10 À1 Pa. Two kinds of metastable phases, with space groups of P6 3 cm and P6 3 /mmc, were found through rapid solidification of an undercooled YbFeO 3 melt in an atmosphere with reduced Po 2 . The crystal structure of the as-solidified samples changed from orthorhombic Pbnm to hexagonal P6 3 cm and P6 3 /mmc with decreasing Po 2 . 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 Fe 21 , which has an ionic radius larger than that of Fe 31 , decreases the tolerance factor and therefore destabilizes the perovskite structure.