Abstract Four tetragonal anisotropic superhard carbon phases, T-C8, T-C12, T-C20 and T-C28 were generated by RG2 program, T-C8 has been reported and named bct-Carbon. The calculated relative enthalpy, elastic constants and phonon dispersion spectra show that these structures are stable. Their lattice failure modes are mainly tensile. Thermodynamic stability, thermal performance and hardness are all in the order T-C20 >T-C8>T-C12>T-C28, which is contrary to the proportion of the four membered ring in the corresponding structure, suggesting that strained four-membered ring is detrimental to the stability and mechanical properties of carbon phases. Among them, T-C20 with hardness of 90.8 GPa is more stable than bct-Carbon and graphite under 20 GPa, suggesting that it is likely to be transformed by cold compressed graphite.

中文翻译：

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三种新的四方超硬 sp3 碳同素异形体

摘要 RG2程序生成了四种四方各向异性超硬碳相T-C8、T-C12、T-C20和T-C28，T-C8已被报道并命名为bct-Carbon。计算的相对焓、弹性常数和声子色散谱表明这些结构是稳定的。它们的晶格失效模式主要是拉伸。热力学稳定性、热性能和硬度的顺序为 T-C20 >T-C8>T-C12>T-C28，这与相应结构中四元环的比例相反，表明应变四元环环不利于碳相的稳定性和机械性能。其中，硬度为90.8 GPa的T-C20在20 GPa下比bct-Carbon和石墨更稳定，表明它很可能被冷压石墨转化。