Crystal Isomers of ScFeO₃

In inorganic compounds, “crystal isomers”, which can exist in metastable phases, are obtained by various solution-processing techniques, high-pressure syntheses, as well as physical and chemical thin film fabrication techniques. The metastable phase depends on the processing, allowing the hierarchy of the Gibbs free energy to be controlled in a phase at a given temperature. In this study, we successfully stabilize five metastable phases, four phases of ScFeO₃ and one Sc_0.48Fe_1.52O₃, prepared from one ScFeO₃ target by the pulsed laser deposition technique. The crystal structures are identified by X-ray diffraction and high-angle annular dark field-scanning transmitted electron microscopy measurements. The relationship between the crystal structure of the film and the substrate is κ-Al₂O₃-type Sc_0.48Fe_1.52O₃ on SrTiO₃(111), spinel-type ScFeO₃ on MgO(001), corundum-type ScFeO₃ on Fe₂O₃/Al₂O₃(0001) and NdCaAlO₄(001), YMnO₃-type ScFeO₃ on Al₂O₃(0001), and bixbyite-type ScFeO₃ on YSZ(001). Four of these structures (all except the bixbyite structure) have not been reported by other processing techniques. These results suggest that the thin film growth technique is a strong tool for exploring novel functional materials and the metastable phases of oxide isomers