Superhard hexagonal sp3-bonded BN polytypes and BC2N from crystal chemistry and first principles

30 August 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

In the framework of a crystallochemical approach, new hexagonal (P63/mc) sp3-bonded BN polytypes (4H, 6H and 8H) and ternary BC2N were proposed by rationalized substitutions of C for B and N in hexagonal carbon allotrope C8 (4C carbon) with cfc topology, and density functional theory calculations of their ground states were performed. All new phases were found to be cohesive and stable mechanically (elastic constants) and dynamically (phonon band structures). According to modern models of hardness, the new phases were recognized as superhard with Vickers hardness above 50 GPa. Their electronic band structures exhibit insulating behavior with large band gaps.

Keywords

BN polytypes
BC2N
DFT
crystal structure
hardness
phonons
band structures

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