Stress reduction in cubic boron nitride by oxygen addition: Explanation of the mechanism by ab-initio simulations

We report ab-initio calculations of the effect of oxygen addition on the characteristics of c-BN. We focus on the lattice constants, bulk modulus, cohesive energy, stress and on the mechanism of stress reduction by oxygen addition. Calculations of cohesive energies are cross-checked by molecular-dynamics simulations. We identify preferred interstitial positions of extra B, N and O atoms trapped in the c-BN(O) lattice. We show that for a given composition the c-BN(O) configurations with interstitial O atoms are energetically preferred over configurations with interstitial B and N atoms, and that the former configurations exhibit lower compressive stress. The results provide a mechanism of the experimentally observed reduction of the stress introduced into c-BN(O) by interstitial B and (mainly) N atoms, based on exchanging places of these atoms and lattice O atoms.