Article ID: M2017106
The structure of C-AlRuNi was determined by single-crystal X-ray diffraction (space group Pm3 (No. 200); a = 0.77088(4) nm; R = 0.0401 for 268 independent reflections (Fo > 2σ(Fo)) measured by Mo Kα radiation). The fundamental structure of C-AlRuNi can be explained by the packing of two types of icosahedra. One is the regular icosahedron of transition metals (TMs; Ru and Ni) with a central TM atom at a 1a site (H-ICO), and the other is the irregular icosahedron of TMs with a central TM atom at a 1b site (HM-iICO). An H-ICO is in contact with six H-ICOs and eight HM-iICOs in the directions of the twofold and threefold axes, respectively. The interstitial spaces among the TM distribution are filled by Al atoms. An HM-iICO contains an Al icosahedron (Al-ICO) inside the HM-iICO and a large Al-cube outside of it. An H-ICO has a small Al-cube inside the H-ICO and an Al distorted icosidodecahedron outside of it, indicating the atomic arrangement associated with a pseudo-Mackay cluster (pMC). The structure of C-AlRuNi can also be explained by the CsCl-like packing of pMCs and Al-ICO clusters. The pMC and Al-ICO are the key clusters for explaining the structures of the C1 and C2 phases in the Al–TM–TM ternary system.