Two Novel C₃N₄ Phases: Structural, Mechanical and Electronic Properties.

Qingyang Fan,Qun Wei,Yintang Yang,Changchun Chai

doi:10.3390/ma9060427

Abstract

We systematically studied the physical properties of a novel superhard (t-C3N4) and a novel hard (m-C3N4) C3N4 allotrope. Detailed theoretical studies of the structural properties, elastic properties, density of states, and mechanical properties of these two C3N4 phases were carried out using first-principles calculations. The calculated elastic constants and the hardness revealed that t-C3N4 is ultra-incompressible and superhard, with a high bulk modulus of 375 GPa and a high hardness of 80 GPa. m-C3N4 and t-C3N4 both exhibit large anisotropy with respect to Poisson’s ratio, shear modulus, and Young’s modulus. Moreover, m-C3N4 is a quasi-direct-bandgap semiconductor, with a band gap of 4.522 eV, and t-C3N4 is also a quasi-direct-band-gap semiconductor, with a band gap of 4.210 eV, with the HSE06 functional.

Highlights

Studies on light element-based materials trace back to the middle of the last century
Lavoisier found that diamond was isostructural to carbon and much denser than graphite, many studies have been devoted to its synthesis under high pressure [1,2,3,4]
Many boron nitride allotropes have been investigated by researchers, such as O-BN, Pbca-BN, Z-BN, W-BN, h-BN, bct-BN, P-BN, and cT8-BN

Summary

Introduction

Studies on light element-based materials trace back to the middle of the last century. More and more researchers have begun to investigate the carbon allotropes [5,6,7,8,9,10,11,12,13,14,15]. The second light element-based material to be evidenced was boron nitride. It includes three different structures: blende-, wurtzite- and graphitic-type structures. Many boron nitride allotropes have been investigated by researchers, such as O-BN, Pbca-BN, Z-BN, W-BN, h-BN, bct-BN, P-BN, and cT8-BN. Interest in carbon nitrides has been initiated by studying materials that exhibit mechanical properties comparable with those of diamond. Gueorguiev et al [17,18]

Methods

Results

Conclusion