Structure truncated triangular

Two limiting structures with four spherons as core or inner core are shown in Figs. 6 and 7. The structure shown in Fig. 6 has the central tetrahedron of four spherons surrounded by a larger tetrahedron of four and a truncated tetrahedron of 12, a total of 16 spherons in the outer layer. The packing is triangular. This is the structure of the cpre for magic number 126. It has double completed-shell character, LN. 

In many cases the octahedron based structures appear with a truncation R = 75%. In that case they can be described as platelets. On the other hand the fact that the growth rate of the various crystal faces might be different generates irregular shaped platelets. A particulary common shape are the triangular plates (shown in Fig. 8). These are the result of truncating a single tetrahedron with ill faces. 

Figure 4.21. Pictures of self-assembled crystals with open structure, (a, b) An array of truncated octahedra, with simple cubic symmetry, (c, d) An array of truncated cubes, with fee symmetry, (e, f) An array of truncated tetrahedra. (g, h) An array of truncated cubes, with bcc symmetry, (i, j) An array of truncated cubes. Each cube in (i, j) has solder on only four of its eight triangular faces. (Reprinted with permission from Science, 1999, 284, 948-951. Copyright 1999 American Association for the...

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... 

---