Figure 4
Shells of the double-Mackay cluster (Sugiyama et al., 1998) building the approximant cP138-α-Al–Mn–Si. The shells (a)–(e) are centred at the origin of the unit cell and shells (a)–(c) in the body centre as well. Shells (a)–(c) form the 54 atom Mackay cluster. (a) Al/Si icosahedron. If the icosahedral symmetry is broken by this innermost shell, the pseudo-Mackay cluster is obtained (Boudard et al., 1992). (b) Al icosidodecahedron. Its pentagons are capped by Mn atoms forming an icosahedron with diameter similar to the icosidodecahedron (c). (d) Complex Al shell. (e) Icosahedral Al/Si shell. |