Synthesis, structure and physical properties of the new uranium ternary phase U3Co2Ge7

A new ternary compound, U3Co2Ge7, has been synthesized from the corresponding elements by a high temperature reaction using molten tin flux. It crystallizes in the orthorhombic La3Co2Sn7-type (Pearsonʹs symbol oC24, space group Cmmm, No. 65) with lattice parameters determined from single-crystal X-ray diffraction as follows: a=4.145(2) Å; b=24.920(7); c=4.136(2) Å, V=427.2(3) Å3. Structure refinements confirm an ordered structure having two crystallographically inequivalent uranium atoms, occupying sites with dissimilar coordination. U3Co2Ge7 orders ferromagnetically below 40 K and undergoes a consecutive magnetic transition at 20 K. These results have been obtained from temperature- and field-dependent magnetization, resistivity and heat-capacity measurements. The estimated Sommerfeld coefficient γ=87 mJ/mol-U K2 suggests U3Co2Ge7 to be a moderately heavy-fermion material.