Crystal structure of the ternary silicide U2RuSi3: a new ordered version of the hexagonal AlB2-type structure

Abstract

The ternary silicide U₂RuSi₃ was prepared from the elemental components in an induction levitation furnace. It was investigated by electron diffraction as well as by X-ray diffractometry on both a single crystal and a powder. The crystal structure was determined from four-circle diffractometer data and refined to a residual of R= 0.026 for 145 reflections and 11 variable parameters. It is of a new type with hexagonal symmetry deriving from the AIB₂ type: P6/mmm, a= 814.8(2) pm, c= 385.5(2) pm, V= 0.2216(2) nm³, Z=2. The silicon and ruthenium atoms are all surrounded by trigonal prisms of uranium atoms and are ordered in a two-dimensional network. The ternary silicide U₂OsSi₃ was found to be isotypic with U₂RuSi₃. At low temperatures, the magnetic susceptibility of U₂RuSi₃ tends towards saturation and characterizes a spin fluctuation behaviour.