Superhard orthorhombic BCN allotropes: oIm12-BCN and oPm12-BCN

The structural, electronic and mechanical properties (elastic, ideal strength and hardness) of two novel superhard boron-carbon-nitride allotropies named as oIm12-BCN and oPm12-BCN were investigated by first-principles calculations. Phonon dispersion calculations indicate that oIm12-BCN and oPm12-BCN are dynamically stable at ambient condition. The results show that oIm12-BCN is more energetically favorable than oPm12-BCN as well as most of the reported BCN compounds. The strength calculations reveal that the failure mode in oIm12-BCN is dominated by the shear type, and the (010)[001] direction is the weakest one with the lowest peak shear stress of 53.1 GPa. In oPm12-BCN, the failure mode is dominated by the shear type, and the (100)[010] direction is the weakest one. Theoretical hardness of oIm12-BCN (74.7 GPa) is evidently greater than that of oPm12-BCN (70.6 GPa), bc-BC4N (67.7 GPa), c-BN (66.4 GPa) and most of the reported BCN phases. The results imply that oIm12BCN and oPm12-BCN are potential superhard materials.

Automated summary

The structural, electronic and mechanical properties of two novel superhard boron-carbon-nitride allotropies, oIm12-BCN and oPm12-BCN, were investigated using first-principles calculations. The results show that oIm12-BCN is energetically favorable and has a higher theoretical hardness than oPm12-BCN and most reported BCN phases. The failure mode in both allotropies is dominated by shear, with specific directions being the weakest.