A study was made of the structural and electronic properties of samples which contained specified vacancies. Five C atoms in the shape of a centered tetrahedron were missing, and twelve C atoms which surrounded the vacancy were replaced by N or B atoms. The bulk modulus of material with substituted N was greater than that in samples without substitution around the vacancy. However, it was still slightly smaller than that of vacancy-free material. The B substitution led to an appreciable relaxation of the atomic positions and to a large reduction in the bulk modulus. The Born criterion for mechanical stability was satisfied in both cases. The calculated electronic structures suggested that the introduction of N atoms around vacancies failed to generate conduction electrons, whereas the introduction of B atoms produced conducting holes.

S.Han, J.Ihm: Physical Review B, 1997, 55[23], 15349-52