The Carbon-Silicon Crystal Unit Cell

Silicon carbide is a relatively simple substance in the sense that its structure and properties are essentially isotropic. In the basic unit cell, each atom of one element is surrounded by a tetrahedron of four atoms of the other element. Each element shares pairs of electrons with the other (the four 2sp orbitals of carbon with the four orbitals of silicon), A schematic representation of the SiC crystal is shown in Fig. 7.1. 

Each SiC unit cell has eight atoms located as follows 1/8 x 8 (silicon) at the comers, 1/2 x 6 (silicon) at the faces and 4 (carbon) inside the unit cube as illustrated in Fig. 7.2t l (for the sake of clarity, only the silicon atoms are shown). In such a stmcture, each atom has a coordination number of four. 

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