Crystal structure and physical properties of the novel ternary intermetallics URuSi3-x and U3Ru2Si7

Two novel ternary intermediate phases, namely URuSi3-x (x=0.11) and U3Ru2Si7 were found in the Si-rich part of the U-Ru-Si phase diagram. Single crystal X-ray diffraction measurements, carried out at room temperature, indicated that URuSi3-x crystallizes in its own tetragonal type structure (space group P4/nmm, no. 129; unit cell parameters: a=12.108(1) A and c=9.810(1) A), being a derivative of the BaNiSn3-type structure. U3Ru2Si7 adopts in turn a disordered orthorhombic La3Co2Sn7-type structure (space group Cmmm, no. 65; unit cell parameters: a=4.063(1) A, b=24.972(2) A and c=4.072(1) A). As revealed by magnetization, electrical resistivity and specific heat measurements, both compounds order magnetically at low temperatures. Namely URuSi3-x is a ferromagnet with TC=45 K, and U3Ru2Si7 shows ferrimagnetic behavior below TC=29 K. - Graphical abstract: Thermal dependence of the specific heat of the novel intermetallics URuSi3 and U3Ru2Si7. The arrows mark temperatures of ferro- or ferrimagnetic phase transitions.