Effects of Oxygen Partial Pressure and Tolerance Factor on Phase Selection of DyMnO3

The equilibrium crystal structure of LnMnO(3) (Ln: lanthanide) has been reported to be orthorhombic when relatively large ions from La3+ to Dy3+ are used as Ln(3+) and hexagonal when relatively small ions from Ho3+ to Lu3+ are used. It has been reported that the hexagonal phase is formed when the tolerance factor, expressed as functions of radii of the constituent ions, is less than 0.840. In the present study, we attempted to induce oxygen deficiency in DyMnO3 under the solidification at low oxygen partial pressure using aerodynamic levitator to reduce the tolerance factor through a decrease in the valence of manganese ions and the accompanying increase in the ionic radius. The results showed that the oxygen deficiency increases with decreasing oxygen partial pressure. Assuming that valence of manganese ions decreased due to the increase in oxygen deficiency, the corresponding tolerance factor evaluated from the average ionic radii of manganese and oxygen decreased, which promoted the formation of the hexagonal phase as is the case with the reduction of the ionic radius of Ln(3+).