A pseudo-tetragonal phase of superhard B8C16(N6CO)

A superhard phase of I-B8C16(N6CO) with pseudo-tetragonal structure is predicted using first-principles calculations. The structural stability, ideal tensile strength, theoretical hardness and chemical bonding of I-B8C16(N6CO) are investigated. The phonon dispersions indicate this phase is dynamically stable at ambient conditions. Enthalpy calculations indicate it is thermodynamically favorable than the previously synthesized tetragonal B8C16(N6CO). The band structure indicates that the predicted I-B8C16(N6CO) is a semiconductor with a direct band gap of about 1 eV. Theoretical hardness demonstrated that I-B8C16(N6CO) is a potential ultra-hard material with a Vickers hardness of about 75 GPa, significantly harder than c-BN. Also, the lowest peak tensile stress is calculated to be 48.7 GPa in the y-axis direction, which is higher than that of recently synthesized superhard material like γ-B28 and BC5. The results provide insight into exploration of the B–C–N–O quaternary superhard materials for potentially technological applications.

► A quaternary phase I-B8C16(N6CO) with seudo-tetragonal structure is proposed.
► I-B8C16(N6CO) is thermodynamically favorable than the previously synthesized S1 structure.
► I-B8C16(N6CO) is a potentially ultra-hard material.