Carbon in boron carbide: The crystal structure of B11.4C3.6

A single crystal of boron carbide obtained from a self-propagating high-temperature synthesis (SHS) product was studied by X-ray crystallography: B11.4C3.6, a = 5.594(2) Å, c = 11.977(7) Å, V = 324.6(7) Å3, space group R3m, Z = 3, ρcalcd = 2.56 g/cm3, R = 0.048. The content of carbon in the single crystal was estimated at ∼24 at % from analysis of the unit cell parameters, bond lengths, and the volume of B12 − xCx icosahedra, which demonstrated the possibility of obtaining by SHS carbon-rich boron carbide crystals due to the substitution of carbon atoms for boron atoms in icosahedra. Comparison of the X-ray crystallographic data for single crystals of boron carbide with the results of quantum-chemical calculations (an ab initio method (the 3–21G basis set) with geometry optimization) showed that the C-B-C group in a crystal has a nonlinear structure.