The limit of non-stoichiometry in silicon carbide

The extent of the silicon carbide single-phase stability field has been investigated. Samples were equilibrated at 2400 ° C by coarsening of fine-grain silicon carbide powder. The lattice parameter, density, and the silicon-to-carbon ratio were measured on silicon- and carbon-saturated samples. These two compositions were not distinguishable at a level of better than one part in one thousand by their molecular weights per mole of crystal sites; no native point defects measurably respond to the difference in silicon activity. The accuracy of the lattice parameter and density measurements require that the free energies of defect pair formation be larger than about 3eV. This applies to antisite pairs, Frenkel pairs and Schottky pairs. It is concluded that silicon carbide is largely stoichiometric. The crystal chemistry must be dominated by electrons, holes and impurities.