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 degrees C, the ternary rare-earth germanides RE3Ru2Ge3 and RE3Ir2Ge3 have been prepared for most of the smaller RE components (RE=Y, Gd-Tm, Lu). In the iridium-containing reactions, the new phases RE2IrGe2 were also generally formed as by-products. Powder X-ray diffraction revealed orthorhombic Hf3Ni2Si3-type structures (space group Cmcm, Z=4) for RE3M2Ge3 (M=Ru, Ir) and monoclinic Sc2CoSi2-type structures (space group C2/m, Z=4) for RE2IrGe2. Full crystal structures were determined by single-crystal X-ray diffraction for all members of RE3Ru2Ge3 (a=4.2477(6) angstrom, b=10.7672(16) angstrom, c=13.894(2) angstrom for RE=Y; a=4.2610(3)-4.2045 (8) angstrom, b=10.9103(8)-10.561(2) angstrom, c=14.0263(10)-13.639(3) angstrom in the progression of RE from Gd to Lu) and for Tb3Ir2Ge3 (a=4.2937(3) angstrom, 6=10.4868(7) angstrom, c=14.2373(10) angstrom). 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 RE3M2Ge3 based on [M2Ge3] layers built from linked MGe4 tetrahedra, which emphasizes the strong M-Ge covalent bonds present. The temperature dependence of the electrical resistivity of RE3Ru2Ge3 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 3 K and several unusual field-dependent transitions suggestive of complex spin reorientation processes. (C) 2013 Elsevier Inc. All rights reserved.