### Pc-carbon:一种可能的超硬碳材料

1. a 西南大学化学化工学院 重庆 400715;
b 中国科学院化学研究所 北京 100190
• 收稿日期:2019-01-09 出版日期:2019-05-15 发布日期:2019-04-02
• 通讯作者: 甘利华 E-mail:ganlh@swu.edu.cn
• 基金资助:

项目受国家自然科学基金（Nos.51472208，51772300）资助.

### Pc-carbon:A Possible Superhard Monoclinic Carbon Allotrope

Cao Ai-Huaa, Wu Bob, Gan Li-Huaa

1. a School of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, China;
b Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
• Received:2019-01-09 Online:2019-05-15 Published:2019-04-02
• Contact: 10.6023/A19010017 E-mail:ganlh@swu.edu.cn
• Supported by:

Project supported by the National Natural Science Foundation of China (Nos. 51472208, 51772300).

In this paper, we predicted a superhard carbon phase (Pc-carbon) by using CALYPSO software. The crystal structure belongs to monoclinic system with the space group Pc. We have studied the electronic and mechanical properties of Pc-carbon by first principles calculations. The calculated total energy per atom of Pc-carbon have a minimum value of -8.08 eV, confirming that the optimized structure is stable. And the minimum total energy per atom of Pc-carbon is higher than diamond and graphite, suggesting that the Pc-carbon should be thermodynamically metastable comparing diamond and graphite. There are no imaginary frequency throughout the entire Brillouin zone in the phonon dispersion, confirming the dynamical stability of Pc-carbon up to 100 GPa. The elastic constants of Pc-carbon follow the Born mechanical stability criteria, demonstrating the mechanical stability of Pc-carbon. The calculated B/G value and Poisson's ratio show that Pc-carbon is brittle. The calculated Vickers hardness value of Pc-carbon is 87.6 GPa, which is much larger than the minimal value for a superhard materials (40 GPa), indicating Pc-carbon is a potential superhard material. The Vickers hardness of Pc-carbon is less than that of diamond and M-carbon, but is comparable to that of bct-C4 and Ibam-C. In addition, the ideal tensile and shear strengths of Pc-carbon (65.8 and 56.5 GPa) are comparable to those of c-BN (55.3 and 58.3 GPa), suggesting that Pc-carbon may have similar tensile and shear resistance to c-BN. The elastic anisotropy index AU is 0.35, indicating that Pc-carbon is elastic anisotropic; the fractional anisotropy ratio of bulk modulus AB and shear modulus AG are 0.010 and 0.032, suggesting that the bulk modulus and shear modulus of Pc-carbon are all elastic anisotropic. The hydrostatic calculations of Pc-carbon indicate that Pc-carbon have excellent incompressibility as the pressure is increased up to 100 GPa. And Pc-carbon is an ultra-incompressible material like other carbon allotropes. The calculated band gap of Pc-carbon is estimated to be 0.99 eV, indicating that Pc-carbon is an indirect band gap semiconductor. The PDOS of Pc-carbon reflects significant sp3 hybridization between atomic orbitals, which leads to the superhard properties of Pc-carbon. Therefore, Pc-carbon is a potential superhard semiconductor material.