Truncated octahedron structure

These are several Fee structures which are based on the octahedron and are illustrated in Fig. 7. In fact the square pyramid is a half-octahedron. The cubo-octahedron structures are obtained from the octahedron by truncations in 100 planes. It is interesting to note that the polyhedra might have different faces in contact with the substrate. 

Figure 4.2. Examples of highly symmetric cluster structures octahedron Mgs, truncated cub-octahedron Mii6, and icosahedron M147.

Figure 14.11 Crystal structure of HPF6.6H2O showing the cavity formed by 24 H2O molecules disposed with their O atoms at the vertices of a truncated octahedron, The PFe octahedra occupy centre and comers of the cubic unit cell, i.c. one PFr, at the centre of each cavily. ...

The linking pattern of two zeolites is shown in Fig. 16.24. They have the /I-cage as one of their building blocks, that is, a truncated octahedron, a polyhedron with 24 vertices and 14 faces. In the synthetic zeolite A (Linde A) the /3-cages form a cubic primitive lattice, and are joined by cubes. j3-Cages distributed in the same manner as the atoms in diamond and linked by hexagonal prisms make up the structure of faujasite (zeolite X). 

Figure 11. The truncated octahedron building block (also termed sodalite cage,f or p-cage ) (a) tetrahedral atoms (usually Si or Al) are located at the corners of the polygons with oxygen atoms halfway between them. Illustration of the linkage, through double four-membered rings, of two truncated octahedra (b) and the structure of zeolite-A (c).

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. 

It was indicated above that Ni38 is a special case. Reactivity experiments52 measuring the saturation coverage of this cluster with N2, H2, and CO molecules suggest that the structure of Ni3g is a truncated octahedron cut from a face-centered cubic (fee) lattice. This structure is shown in... 

From a geometrical point of view only, this structure could be compared with that of CsCl, with 1 Ca in place of Cs, and the centre of a 6 B octahedron in place of the Cl atom (in the centre of the cell with its axes parallel to the cell axes). Ca is surrounded by 24 B in a regular truncated cube (octahedra and truncated cubes fill space). A number of hexaborides (of Ca, Sr, Ba, Y and several lanthanides and Th, Np, Pu, Am) have been described as pertaining to this structural type. 

Structure. We have simulated MTHP in isolation and in an infinitely diluted aqueous solution (56 water molecules in a truncated octahedron). The average position value of (01-Cl-05-C6) is 85 in isolation and 75 in water. Previous calculations... 

Figure 15-4. Structures of some zeolites a) basket-like unit (truncated octahedron) of linked Si04 tetrahedra b) framework of baskets as in a), joined at square faces c) space-filling framework of truncated octahedra and cubooctahedra.

The secondary structure unit in zeolites A. X, and V is the truncated octahedron. These polyhedral units are linked in three-dimensional space through the four- or six-membered rings, The former linkage produces the zeolite A structure, and the latter the topology of zeolites X and Y and of the mineral faujasite. 

In order to arrive at the distribution of different sites on the particles, one must adopt a certain shape. Carlsson et al. assumed that the particles are truncated octahedrons (see Fig. 7.8), where the dark part corresponds to a supported particle of fee structure, with edges of four atoms long, and five atom layers thick. This... 

Fig. 4. Line representations of zeolite structure (a) sodalite cage, or truncated octahedron (b) type A zeolite unit cell (c) unit cell of types X and Y, or faujasite (d) cation sites in type A (there are 8 1,3 II, and 12 III sites per unit cell) (e) cation sites in types X and Y (161,32 Y, 32 II, 32 IT, 48 III, and 32 IIT, sites per unit cell).

Figure 6 TEM characterization of the structure and morphology of Pd nanoparticles supported on MgO(l 0 0). (a) Electron diffraction pattern (b) top-view micrograph (c) profile view micrograph of an individual particle (d) drawing of the truncated octahedron shape of a Pd particle (e) shape of a large coalesced particle (0 truncated pyramid shape of a small (<7 nm) Pd particle.

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