Hexagonal net

The carbon sheets form hexagonal nets, each of which is displaced with respect to the one below. 

A simple structure which can be described in terms of superposition of (even if far away, not close-packed) hexagonal layers is that of graphite Chyt C%u The hexagonal net is also called graphitic net. 

Figure 3.25. Stacking symbols applicable to larger unit cells. A, B, C three nodes in the unit cell of a triangular net a, b, c six nodes of a hexagonal net in the unit cell a, 3, p nine nodes of a kagome net in the unit cell. The coordinate doublets are indicated.

The AlB2-type structure can be considered a filled-up WC structure type. The B atoms form a hexagonal net and centre all the A1 trigonal prisms. The arrangement of the boron atoms in their layers is the same as that of carbon in graphite (63 layers). (See also the nThSi2, tI12, description for a comparison between the planar... 

Equal numbers of Na and As atoms form hexagonal nets (as in boron nitride), the remaining Na atoms are arranged in layers on either sides of these nets. 

Perpendicular linkage from simple hexagonal net. Am. Mineral., 62 (7-8), 703-709. 

Example 16.1-1 Find the Bravais lattices, crystal systems, and crystallographic point groups that are consistent with a C3z axis normal to a planar hexagonal net. 

Figure 16.6. Primitive unit cell of the rhombohedral lattice 3 R. The three fundamental translations a1 a2, a3 are of equal length and make equal angles with e3. Hexagonal nets in four successive layers show how the rhombohedral cell may be constructed.

Exercise 16.1-1 Could a different lattice be generated by placing P/ over P3 and P2, respectively, in the second and third layers of a hexagonal net ... 

Example 16.3-2 Find the reciprocal lattice of the planar hexagonal net which has the primitive unit cell shown in Figure 16.10. 

The direct lattice and reciprocal lattice unit cells are marked on the crystal pattern of a planar hexagonal net in Figure 16.10, using eqs. (13), (14), and (18). The scales chosen for... 

In a similar way Kekule s theory of the benzene structure has been very completely established by the whole development of aromatic chemistry. The direct physical verification of the presumably planar arrangement was in this case more delayed. The crystal structure of graphite was examined almost as soon as that of diamond, but the early results were inconclusive. The structure is not determined by the symmetry alone, and the later detailed investigation by Bernal (1924) showed that the carbon atoms in the hexagonal net must be coplanar to within at least 0-38 A. Later work by Ott (1928) narrowed this limit still further. Although it is generally assumed that the atoms are coplanar, the exactness with which this can be established depends on... 

Figure 2. Model of a spherical hexagonal net with equal edges and with icosahedral... 

If the formula of orthorhombic black phosphorus is written simply as P, then Z = 8. The special positions of space group Cmca are 4(a) 2/m, 4(b) 2/m, 8(c) 1,8(d) 2, 8(e) 2, 8(f) m, and general position 16(g) 1. The independent P atom actually is located in 8(f), generating a continuous double-layer structure, which is a heavily puckered hexagonal net in which each P atom is covalently bound to three others within the same layer. In Fig. 9.6.12, two puckered layers in... 

Si layers Polymeric unit [Si ] in CaSi2 consists of corrugated layers of six-membered rings, as shown in Fig. 14.4.3(e). In /3-ThSii, the [Si ] units form planar hexagonal nets, which are similar to the B layers in A1B2 [Fig. 13.3.1(f)],... 

The structure of ZrCI consists of layers of metal atoms in graphite-like hexagonal nets. ... 

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