Ternary rare-earth ruthenium and iridium germanides RE 3 M 2Ge3 (RE=Y, Gd–Tm, Lu; M=Ru, Ir).

Through arc-melting reactions of the elements and annealing at 800°C, the ternary rare-earth germanides RE 3Ru2Ge3 and RE 3Ir2Ge3 have been prepared for most of the smaller RE components (RE=Y, Gd–Tm, Lu). In the iridium-containing reactions, the new phases RE 2IrGe2 were also generally formed as by-products. Powder X-ray diffraction revealed orthorhombic Hf3Ni2Si3-type structures (space group Cmcm, Z=4) for RE 3 M 2Ge3 (M=Ru, Ir) and monoclinic Sc2CoSi2-type structures (space group C2/m, Z=4) for RE 2IrGe2. Full crystal structures were determined by single-crystal X-ray diffraction for all members of RE 3Ru2Ge3 (a=4.2477(6)Å, b=10.7672(16)Å, c=13.894(2)Å for RE=Y; a=4.2610(3)–4.2045(8)Å, b=10.9103(8)–10.561(2)Å, c=14.0263(10)–13.639(3)Å in the progression of RE from Gd to Lu) and for Tb3Ir2Ge3 (a=4.2937(3)Å, b=10.4868(7)Å, c=14.2373(10)Å). Both structures can be described in terms of CrB- and ThCr2Si2-type slabs built from Ge-centred trigonal prisms. However, band structure calculations on Y3Ru2Ge3 support an alternative description for RE 3 M 2Ge3 based on [M 2Ge3] layers built from linked MGe4 tetrahedra, which emphasizes the strong M–Ge covalent bonds present. The temperature dependence of the electrical resistivity of RE 3Ru2Ge3 generally indicates metallic behaviour but with low-temperature transitions visible for some members (RE=Gd, Tb, Dy) that are probably associated with magnetic ordering of the RE atoms. Anomalously, Y3Ru2Ge3 exhibits semiconductor-like behaviour of uncertain origin. Magnetic measurements on Dy3Ru2Ge3 reveal antiferromagnetic ordering at 3K and several unusual field-dependent transitions suggestive of complex spin reorientation processes. [ABSTRACT FROM AUTHOR]