Energetics of segregation in β-C2BN

We show that β-phase boron–carbon–nitrogen $({\mathrm{C}}_{\mathrm{2}}\mathrm{BN})$ structures energetically favor segregation into superlattices of alternating diamond and cubic boron nitride $\mathrm{(c}\mathrm{BN})$ layers. Local-density functional calculations of total energies using pseudopotential approximations and a plane-wave basis set of the $\mathrm{\beta -}{\mathrm{C}}_{\mathrm{2}}\mathrm{BN}$ systems with different thicknesses of alternating diamond and $c\mathrm{BN}$ layers grown along the (001) direction found a decrease in the formation energy with an increase in the layer thickness. We consider this phenomenon to be a result of the charge redistribution in each layer due to interface formation. Our study indicates that the deviation of charge distributions from those in pure diamond and $c\mathrm{BN}$ structures due to the existence of BN–C junctions in $\mathrm{\beta -}{\mathrm{C}}_{\mathrm{2}}\mathrm{BN}$ may result in difficulties in its synthesis.