Thermally induced hex-graphene transitions in 2D carbon crystals

Ran Fu,Yuequn Fu,Yanwen Lin,Yisi Liu,Yuanhao Chang,Yihua Xu,Zhisen Zhang,Ke Xu,Jianyang Wu

doi:10.1515/ntrev-2022-0066

Abstract

Abstract Resourceful beyond-graphene two-dimensional (2D) carbon crystals have been proposed/synthesized; however, the fundamental knowledge of their melting thermodynamics remains lacking. Here, the structural and thermodynamic properties of nine contemporary 2D carbon crystals upon heating are investigated using first-principle-based ReaxFF molecular dynamics simulations. Those 2D carbon crystals show distinct evolution of energetic and Lindemann index that distinguish their thermal stabilities. There are two or three critical temperatures at which structural transformation occurs for non-hexagon-contained 2D carbon allotropes. Analysis of polygons reveals that non-hexagon-contained 2D carbon crystals show thermally induced hex-graphene transitions via mechanisms such as bond rotations, dissociation, and reformation of bonds. The study provides new insights into the thermodynamics and pyrolysis chemistry of 2D carbon materials, as well as structural transitions, which is of great importance in the synthesis and application of 2D materials in high-temperature processing and environment.

Highlights

Carbon is a unique element because it plays a crucial role in the chemistry of living things
This study provides critical insights into the melting thermodynamics and pyrolysis chemistry of 2D carbon crystals, which sheds light on the synthesis and applications of 2D carbon allotropes and offers guidance for heat-resistant composite designs by 2D carbon crystals
With regard to 2D carbon crystals of penta-graphene and S-graphene who possess the highest E at ground state; their E–T curves are highlighted by double drops of E at two critical T

Summary

Introduction

Carbon is a unique element because it plays a crucial role in the chemistry of living things. Graphene ushers a new era of twodimensional (2D) materials It is a quasi 2D monolayered structure of carbon atoms that has attracted particular attention due to its unique electronic properties [5], as well as its outstanding strength, elasticity, and flexibility [6]. Due to the fact that rather high energy of around 5.0 eV is required to break a sp2-hybrid C–C bond of graphene [7], it exhibits excellent resistance to mechanical and thermal actions suggesting its extremely high fusing degree. This mainly stems from the arrangement of the sp2-hybrid carbon atoms in a hexagonal honeycomb structure [8]. There are other 2D materials such as 2D MoS2 [9–15] and 2D SiC [16] that have attracted great attentions due to their unique mechanical properties [12,17,18], electrical conductivity [9], and thermal stability [16,19]

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