Ternary rare-earth ruthenium and iridium germanides RE3M2Ge3 (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 3 Ru 2 Ge 3 and RE 3 Ir 2 Ge 3 have been prepared for most of the smaller RE components ( RE =Y, Gd–Tm, Lu). In the iridium-containing reactions, the new phases RE 2 IrGe 2 were also generally formed as by-products. Powder X-ray diffraction revealed orthorhombic Hf 3 Ni 2 Si 3 -type structures (space group Cmcm , Z =4) for RE 3 M 2 Ge 3 ( M =Ru, Ir) and monoclinic Sc 2 CoSi 2 -type structures (space group C 2/ m , Z =4) for RE 2 IrGe 2 . Full crystal structures were determined by single-crystal X-ray diffraction for all members of RE 3 Ru 2 Ge 3 ( a =4.2477(6) A, b =10.7672(16) A, c =13.894(2) A for RE =Y; a =4.2610(3)–4.2045(8) A, b =10.9103(8)–10.561(2) A, c =14.0263(10)–13.639(3) A in the progression of RE from Gd to Lu) and for Tb 3 Ir 2 Ge 3 ( a =4.2937(3) A, b =10.4868(7) A, c =14.2373(10) A). Both structures can be described in terms of CrB- and ThCr 2 Si 2 -type slabs built from Ge-centred trigonal prisms. However, band structure calculations on Y 3 Ru 2 Ge 3 support an alternative description for RE 3 M 2 Ge 3 based on [ M 2 Ge 3 ] layers built from linked M Ge 4 tetrahedra, which emphasizes the strong M –Ge covalent bonds present. The temperature dependence of the electrical resistivity of RE 3 Ru 2 Ge 3 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, Y 3 Ru 2 Ge 3 exhibits semiconductor-like behaviour of uncertain origin. Magnetic measurements on Dy 3 Ru 2 Ge 3 reveal antiferromagnetic ordering at 3 K and several unusual field-dependent transitions suggestive of complex spin reorientation processes.