Phase transition of Ln3IrO7 (Ln = Pr, Nd, Sm, Eu) and its low-temperature structure

Ternary lanthanide iridium oxides Ln(3)IrO(7) (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 Ln(3)IrO(7) (Ln = Pr, Nd, Sm, and Eu) at 262, 342, 420, and 485 K, respectively. At low temperatures, Ln(3)IrO(7) crystallizes in a monoclinic structure with the space group P2(1)/n. These results for Ln(3)IrO(7) are compared with those for Ln(3)MoO(7), Ln(3)RuO(7), Ln(3)ReO(7), and Ln(3)O(S)O(7).