Theoretical study on the controllable preparation of superhard BC2N under high pressure

Abstract

High-density B–C–N ternary compounds have attracted considerable attention due to their potential and excellent properties combined with diamond and cubic boron nitride (cBN). However, the development of B–C–N is restricted due to the lack of an ideal precursor with a graphite-like structure. Recently, graphite/hBN superlattices have been synthesized, of which two specific atomic structures have been determined. Here, we simulated the phase transformation of these two graphite/hBN superlattices under high pressure. Results revealed that the puckering pattern of graphite-like layers (i.e., armchair or boat like) can be controlled by adjusting the pressurization process to achieve customized phase transition results, resulting in five different superhard BC₂N compounds. Among these compounds, only R3m-BC₂N, R3m-BC₂N-2, and Rm-BC₂N are diamond-like structures consisting of six-membered rings, while P2/m-BC₂N and P2/m-BC₂N-2 have different structures with additional 4+8 rings due to the varying bonding processes. Band structure analysis revealed that these structures are semiconductors with band gaps in the range of 2.6–4.6 eV. Their theoretical hardness of 70–78 GPa exceeds that of cBN. This simulation study provides insights for the controllable preparation of high-density phase BC₂N compounds and demonstrates the great potential of variable speed pressurization techniques for the discovery of new materials.