Crystal structures of five compounds in the aluminium-ruthenium-silicon system.

Single crystals of five compounds with approximate compositions ∼Ru 16 (Al 0.78 Si 0.22 ) 47 , (I), ∼Ru 9 (Al 0.70 Si 0.30 ) 32 , (II), ∼Ru 10 (Al 0.67 Si 0.33 ) 41 , (III), ∼Ru(Al 0.57 Si 0.43 ) 5 , (IV), and ∼Ru 2 (Al 0.46 Si 0.54 ) 9 , (V), were obtained from polycrystalline lumps mainly composed of the target compounds, and their crystal structures were determined by means of single-crystal X-ray diffraction. The crystal structure of (I) can be related to that of a cubic rational crystalline approximant to an icosa-hedral quasicrystal through crystallographic shear and then unit-cell twinning. The crystal structure of (II) is isotypic with that of a phase with composition ∼Fe 9 (Al,Si) 32 . The crystal structure of (III) is comprised of edge-sharing Ru(Al,Si) 9-11 polyhedra with disordered chains along edges of polyhedra. The crystal structure of (IV) is of the LiIrSn 4 type. The crystal structure of (V) can be viewed as a crystallographic shear structure derived from that of (IV).