Phase Transition of Ln₃IrO₇ (Ln=Pr, Nd, Sm, Eu) and its Low-Temperature Structure

抄録

Ternary lanthanide iridium oxides Ln₃IrO₇ (Ln=Pr, Nd, Sm, and Eu) were prepared and their structures were determined by X-ray diffraction measurements. At room temperature, Pr₃IrO₇ crystallizes in an orthorhombic superstructure of cubic fluorite with the space group Cmcm. The results of the differential thermal analysis (DTA) and specific heat measurements show the existence of a phase transition for Ln₃IrO₇ (Ln=Pr, Nd, Sm, and Eu) at 262, 342, 420, and 485 K, respectively. At low temperatures, Ln₃IrO₇ crystallizes in a monoclinic structure with the space group P2₁/n. These results for Ln₃IrO₇ are compared with those for Ln₃MoO₇, Ln₃RuO₇, Ln₃ReO₇, and Ln₃OsO₇.