Friauf-polyhedron

Figure 7. The Friauf polyhedron. It consists of 12 smaller atoms at the comers of a truncated tetrahedron, which has four hexagonal faces and four triangular faces, and a larger atom at the center. In condensation, hexagonal faces are shared.

Metals can pack in myriad ways in the formation of alloys and intermetallic compounds. An interesting structural unit is the Friauf polyhedron (Figure 7), first reported by Friauf for the copper atoms in the 24-atom face-centered compound MgCu2 [73]. It consists of... 

The Friauf polyhedron consists of a truncated tetrahedron, which has four triangular and four hexagonal faces, around a central position. The next shell is a regular tetrahedron with atom positions out of the hexagonal faces such that the outer shell has 28 triangular faces and 16 corners [12]. Friauf polyhedra are prominent structural elements in the cubic p-Al3Mg2 phase, which has a lattice constant of 2.82 nm and 1168 atoms per unit cell [14]. In this structure, the central position is occupied by a Mn atom, the truncated tetrahedron is occupied by 12 A1... 

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