Influence of some substitutional defects on the relative stability and cohesive properties of cubic boron nitride

Substitutional defects C, Si, Al and Ti included in c-BN are examined using ab initio calculations employing various sizes of supercell to simulate the dependence of the electronic properties on defect concentration. We suggest some of these defects may be readily absorbed into c-BN occupying either of the B and N lattice sites. However, apart from C, the rate of defect solubility markedly changes with defect concentration. The change in compressibility as measured by a substantial lowering of the Bulk Modulus strongly suggests that there would be a related softening of c-BN critically depending on the nominal defect concentration and the chemical character of the defect.