Crystal structure and some magnetic properties of novel compounds: U 3Pt 23Si 11, U 3Pt 5Si and U 6Pt 30Si 19

Abstract

Three new compounds have been found in the U–Pt–Si ternary system, U 3Pt 23Si 11, U 3Pt 5Si and U 6Pt 30Si 19. 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 U 3Pt 23Si 11, formerly reported as U 2Pt 15Si 7, crystallizes in the cubic space group F m 3 ¯ 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. U 3Pt 5Si 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 Ce 3Pd 5Si, from which it only differs by a partial disorder of one Pt-atom site. The dc-magnetic measurement revealed that U 3Pt 5Si orders antiferromagnetically at T N = 11(1) K. U 6Pt 30Si 19 crystallizes in the hexagonal space group P6 3/ 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, R n ( n + 1 ) T 6 ( n 2 + 1 ) M 4 n 2 + 3 , where R stands for f-metal, T for d-transition metal and M for the main-group element.