Crystal structure and some magnetic properties of novel compounds: U3Pt23Si11, U3Pt5Si and U6Pt30Si19

Three new compounds have been found in the U-Pt-Si ternary system, U3Pt23Si11, U3Pt5Si and U6Pt30Si19. They were prepared by reaction of the elemental components in an arc-melting furnace followed by heat-treatment at 900 °C for several days. Their chemical composition was checked by scanning electron microscopy and by energy dispersive spectroscopy. Their crystal structure was determined by single crystal X-ray diffraction techniques. The compound U3Pt23Si11, formerly reported as U2Pt15Si7, crystallizes in the cubic space group Fm3¯m, with a unit-cell parameter at room temperature, a = 16.8341(3) Å. The most striking feature of the structure is the occurrence of octahedral clusters of uranium with short U-U bonds of 3.004(2) Å. U3Pt5Si crystallizes in the orthorhombic space group Imma, in a cell of dimension at room temperature a = 7.1733(3) Å, b = 12.9671(6) Å and c = 7.3578(3) Å. Its crystal structure is closely related to that of Ce3Pd5Si, from which it only differs by a partial disorder of one Pt-atom site. The dc-magnetic measurement revealed that U3Pt5Si orders antiferromagnetically at TN = 11(1) K. U6Pt30Si19 crystallizes in the hexagonal space group P63/m, in a cell of dimension at room temperature a = 15.9377(2) Å and c = 3.9874(1) Å. It belongs to a large family of ternary alloys obeying the general formula, Rn(n+1)T6(n2+1)M4n2+3, where R stands for f-metal, T for d-transition metal and M for the main-group element.