Structure of diamond

There is considerable evidence in the thermoset literature that the fracture energy decreases with increasing crosslink density, consistent with the intuitive result that crosslinking inhibits flow. In the limit of very high crosslink density, where for example we approach the structure of diamond, fracture can occur on a single crystal plane such that... 

Figure 8.3 Structure of diamond showing the tetrahedral coordination of C the dashed lines indicate the cubic unit cell containing 8 C atoms.

Furthermore, spz bonding is connected with tetrahedral bond angles (as in Figure 16-11). These expectations are consistent with the experimentally determined structure of diamond, shown in Figure 17-2. 

Graphite is another solid form of carbon. In contrast to the three-dimensional lattice structure of diamond, graphite has a layered structure. Each layer is strongly bound together but only weak forces exist between adjacent layers. These weak forces make the graphite crystal easy to cleave, and explain its softness and lubricating qualities. 

FIGURE 5.21 The structure of diamond, Each sphere represents the location of the center of a carbon atom. Each atom is at the center of a tetrahedron formed hy the sp1 hybrid covalent bonds to each of its four neighbors. 

FIGURE 14.30 Structure of diamond. Each carbon atom is sp hybridized and forms tetrahedral rr-bonds to four neighbors. This pattern is repeated throughout the crystal and accounts for diamond s great hardness. 

The compact structure of diamond accounts for its outstanding properties. It is the hardest of all materials with the highest thermal conductivity. It is the most perfectly transparent material and has one of the highest electrical resistivities and, when suitably doped, is an outstanding semiconductor material. The properties of CVD and single-crystal diamonds are summarized in Table 7 2.[1][18]-[20]... 

Silicon has the crystal structure of diamond and its properties are influenced by the crystal orientation. ] CVD silicon can be... 

The structures of diamond, silicon, germanium and tin are discussed in Chapter 12. 

FIGU RE 13.12 The structure of diamond showing four covalent bonds to each carbon atom. 

To melt the giant structure of diamond, very strong covalent bonds (1) between carbon atoms (1) must be broken. In contrast, only weak van der Waals forces (1) between iodine (I2) molecules (1) need to be broken when iodine is heated beyond its melting temperature. The strong covalent bonds within the iodine molecules are not affected. 

Figure 4. Influence of three-fold astigmatism, A3, on HRTEM images of diamond in [110] orientation (left A3 = 2250 nm right A3 < 50 nm). When the 3-fold astigmatism is corrected, the HRTEM image shows the dumbbell-structure of diamond, whereas strong 3-fold astigmatism results in an image that cannot be directly interpreted in terms of the atomic...

Fig. 4.3 (a) Crystal structure of diamond and (b) the smallest nanodiamond adamantine... 

Two later sections (1.6.5 and 1.6.6) look at the crystalline structures of covalently bonded species. First, extended covalent arrays are investigated, such as the structure of diamond—one of the forms of elemental carbon—where each atom forms strong covalent bonds to the surrounding atoms, forming an infinite three-dimensional network of localized bonds throughout the crystal. Second, we look at molecular crystals, which are formed from small, individual, covalently-bonded molecules. These molecules are held together in the crystal by weak forces known collectively as van der Waals forces. These forces arise due to interactions between dipole moments in the molecules. Molecules that possess a permanent dipole can interact with one another (dipole-dipole interaction) and with ions (charge-dipole interaction). Molecules that do not possess a dipole also interact with each other because transient dipoles arise due to the movement of electrons, and these in turn induce dipoles in adjacent molecules. The net result is a weak attractive force known as the London dispersion force, which falls off very quickly with distance. 

Figure 9.1. Crystal structure of diamond, (a) Three-dimensional representation ...

The crystalline structure of diamond is best illustrated by using sticks to represent the covalent bonds. It is the molecular nature of diamond that is responsible for this material s unusual properties, such as its extreme hardness. 

Fig. 7.1 Unit cell of the structure of diamond (carbon). Note the tetrahedral (rp3) configuration about each atom. Cf. Fig. 4.2b. [From Ladd. M. F. C. Structure and Bonding in SoUd State Chemistry Ellis Horwood Chicester, 1979. Reproduced with permission.]...

The structure of diamond, a covalent crystal, is shown in Fig. 7.1. How is it related to tome cf the structures cf ionic compounds discussed in this chapter1 ... 

The element carbon occurs in nature in two so-called allotropic forms, different crystal structures with the same chemical formula. In Fig. 3.13 the crystal structure of diamond and graphite have been represented. In diamond the C atoms are closely packed and each C atom is linked with four other C atoms. Thus a tight network of atoms is formed which, together with the binding strength, is responsible for the extreme hardness of diamond. Graphite has a layered structure and the space between the layers is relatively large. 

The classical valency concept of the tetrahedral carbon atom has been more than fully verified by its success in explaining the chemistry of countless thousands of organic compounds. The first direct physical confirmation of the tetrahedral distribution of carbon valency bonds, however, came with the elucidation of the structure of diamond by W. H. and W. L. Bragg (1913) using the newly discovered method of X-ray diffraction. 

Figure 4.13. The 3 2PT structure of diamond. The packing (P) layers are in a ccp pattern. All sites are occupied by C, but here the balls in the T layers are lighter. The cubic unit cell is outlined by double lines.

The shapes of covalent molecules are determined by the number of valence electrons and orbitals available, giving H2, BF3, CH4, NH3, PH3, H20, HF, C1F, PF5, SF6, and IF7. Carbon has four valence electrons and four orbitals, so tetrahedral sp3 bonding dominates the chemistry of carbon. This matches the three-dimensional bonding in zinc blende (3 2PT), and it is the structure of diamond with carbon in P and T layers. 

The structure of diamond is like the zinc blende structure except that all of the atoms are carbon. Calculate the lattice parameter of diamond if the atomic diameter of carbon is 0.92 nm. 

The crystal structure of diamond. Each carbon atom is covalently bonded to four others. 

The three-dimensional network structure of diamond can be considered as constructed from the linkage of nodes (C atoms) with rods (C-C bonds) in a tetrahedral pattern. From the viewpoint of crystal engineering, in a diamondoid network the node can be any group with tetrahedral connectivity, and the linking rods (or linker) can be all kinds of bonding interactions (ionic, covalent, coordination, hydrogen bond, and weak interactions) or molecular fragment. 

The FAU framework structure is composed of sodalite cages, linked by 6-6 secondary building units (SBUs) like the carbon atom in the structure of diamond. The formed cube has an axis, a 24.3 A, and the framework produced by the union of these cubes contains windows, which lead to an approximately spherical cavity with a radius, R 6.9 A, known as the supercage or (1-cagc [108,109], These supercages have tetrahedral symmetry, and are opened through four 12-member ring (MR) windows, each with a diameter of d 1A A [108,109],... 

Figure 2. Idealized crystal structures of diamond and graphite...

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