Superhard sp2–sp3 hybridized B2C3N2 with 2D metallicity

Abstract

Ternary boron–carbon–nitrogen (B–C–N) compounds are considered to possess hardness comparable to diamond and thermal stability comparable to c-BN. Explorations for desirable B–C–N phases have been continuous. However, the nonconductive properties of most B–C–N compounds narrow the applications of these compounds. Herein, we propose a sp²–sp³ hybridized phase of t-B₂C₃N₂, which consists of diamond-like BC blocks connected with single N–N bonds. Elastic constants and phonon dispersion curves confirm that t-B₂C₃N₂ is mechanically and dynamically stable. The structure processes 2D metallicity in a strong 3D network. Furthermore, hardness and electron–phonon calculations reveal that t-B₂C₃N₂ is superhard and superconductive with a superconducting critical temperature reaching 2.3 K.