First-principles study of a novel superhard boron nitride phase

TL;DR

This study predicts a new superhard boron nitride phase, Z-BN, with high stability, transparency, and hardness comparable to c-BN, using first-principles density functional theory calculations.

Contribution

It introduces Z-BN as a novel superhard BN phase with detailed structural, electronic, and mechanical properties predicted via first-principles calculations.

Findings

Z-BN is more energetically favorable than bct-BN.

Z-BN has a high Vickers hardness of 55.88 GPa.

Z-BN can potentially be synthesized at low pressure (~3.3 GPa).

Abstract

A superhard boron nitride phase dubbed as Z-BN is proposed as possible intermediate phase between h-BN and zinc blende BN (c-BN), and investigated using first-principles calculations within the framework of the density functional theory. Although the structure of Z-BN is similar to that of bct-BN containing four-eight BN rings, it is more energy favorable than bct-BN. Our study reveals that Z-BN, with a considerable structural stability and high density comparable to c-BN, is a transparent insulator with an indirect band gap about 5.27 eV. Amazingly, its Vickers hardness is 55.88 Gpa which is comparable to that of c-BN. This new BN phase may be produced in experiments through cold compressing AB stacking h-BN due to its low transition pressure point of 3.3 GPa.