Crystal structure of the 2/1 cubic approximant Ag42In42Yb16

The crystal structure of the 2/1 cubic approximant Ag42In42Yb16 was determined by single crystal X-ray diffraction. The structure model has the composition of Ag40.42In44.50Yb15.08 with a = 24.8687 Å, space group Pa3¯ (No. 205). Among the 14 independent Ag, 13 In, and 5 Yb sites, 6 Ag sites and 6 In sites are icosahedrally coordinated, whereas two sites (In13, Yb1) are Frank-Kasper polyhedrally coordinated. Four Yb sites (Yb2–5) are double pentagonal antiprisms. The basic structural unit can be described as a 102-atom pseudo-Bergman cluster with three successive shells, of which the second shell consists of a dodecahedron and an only nine-atom polyhedron that breaks icosahedral symmetry.