Lattice structure, silicon carbide

Silicon carbide, the simplest silicon-carbon compound, is especially stable. Its typical form, p SiC, has a diamond structure with a lattice constant a = 435 pm (the value for diamond is 356 pm). Each Si atom is surrounded by four C atoms, and every C atom, by four Si atoms. The density (3.17 g/cm ) is lower than that of diamond (3.51 g/cm ) the greater atomic weight of sihcon is more than compensated by its greater lattice constant. The melting point of SiC is 2700 °C (partial decomposition) that of diamond is 3500 ""C. 

Carbosilanes are compounds in which the elements silicon and carbon alternate in the molecular skeleton [1]. Just as the alkanes are formally derived from the diamond lattice and the aromatics from the graphite lattice, the carbosilanes are structurally derived from silicon carbide. Because of the tetravalent nature of silicon and carbon we can expect stable linear, cyclic and polycyclic compounds to occur. However, carbosilanes do not exist in nature. 

There are two types of deviations from the stoichiometric composition in the crystals of silicon carbide polytypes. The first one is characterized by big deviations (Table 1), and it is supposed that it is caused by structural regulation of silicon and carbon vacancies in the crystal lattice. The Si—C layers in cubic and hexagonal positions keep their composition in different... 

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