Abstract
The crystal structure of DyMnO3 (Ln: lanthanide) in the equilibrium state has been reported to be orthorhombic when La3+ to Dy3+, and hexagonal when Ho3+ to Lu3+, are used as Ln3+. However, Kumar et al. reported a two-phase structure of orthorhombic and hexagonal phases is formed in DyMnO3 when it was solidified from an undercooled melt under containerless conditions. To investigate the reason for the formation of this two-phase structure in DyMnO3, the nucleation temperature Tn and the post-recalescence temperature Tpr were measured for the Dy2O3-Mn2O3 system as a function of the substitution ratio for Mn and Dy, x = NMn/(NDy+NMn). As a result, the phase constitution was found to depend on Tn and the amount of undercooling ΔT(=Tpr - Tn) ; h-DyMnO3 is formed when ΔT is small, and o-DyMnO3 is formed when ΔT is large. Furthermore, when Tn is higher than 1530 K, which is the equilibrium temperature at oxygen partial pressure of atmospheric gas at 105 Pa for the chemical reaction of DyMnO3 + 1/3Mn3O4 + 1/3O2 = DyMn2O5, h-DyMnO3 is formed at x(0.5, while h-DyMnO3 is suppressed at x)0.5, irrespective of Tn.
