Wu Qinghua, Hu Qianku, Hou Yiming, Wang Haiyan, Zhou Aiguo, Wang Libo
School of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, People's Republic of China.
J Phys Condens Matter. 2018 Sep 26;30(38):385402. doi: 10.1088/1361-648X/aada2c. Epub 2018 Aug 14.
Using the ab initio evolutionary algorithm, four thermodynamically stable CN phases ([Formula: see text], [Formula: see text]-1, [Formula: see text]-2 and C2/m) are uncovered. The structures of the [Formula: see text], [Formula: see text]-1 and [Formula: see text]-2 phases possess layered features. The dense C2/m phase with 3D strong covalent bond network is calculated to be superhard with hardness of 75.4 and 83.9 GPa by Chen and Gao models. The electronic properties of the CN is diverse including conductor ([Formula: see text]), indirect semiconductor ([Formula: see text]-1 and [Formula: see text]-2) and direct semiconductor (C2/m). Pressure-induced phase transition sequences and critical pressure points are calculated to be [Formula: see text] → [Formula: see text]-1 → [Formula: see text]-2 at 2.7 and 34 GPa, respectively. Though the C2/m phase is metastable at zero temperature, our established pressure-temperature phase diagram of CN shows that the C2/m becomes stable under high temperatures and pressures. The pressure-temperature phase diagram will give theoretical guidance for further experimental synthesis of different CN phases.
使用从头算进化算法，发现了四种热力学稳定的碳氮化物相（[化学式：见原文]、[化学式：见原文]-1、[化学式：见原文]-2和C2/m）。[化学式：见原文]、[化学式：见原文]-1和[化学式：见原文]-2相的结构具有层状特征。通过陈和高模型计算得出，具有三维强共价键网络的致密C2/m相超硬，硬度分别为75.4和83.9吉帕。碳氮化物的电子性质多样，包括导体（[化学式：见原文]）、间接半导体（[化学式：见原文]-1和[化学式：见原文]-2）和直接半导体（C2/m）。计算得出压力诱导的相变序列和临界压力点分别为在2.7吉帕和34吉帕时，[化学式：见原文]→[化学式：见原文]-1→[化学式：见原文]-2。尽管C2/m相在零温度下是亚稳的，但我们建立的碳氮化物压力-温度相图表明，C2/m相在高温高压下变得稳定。该压力-温度相图将为进一步实验合成不同的碳氮化物相提供理论指导。
