High-Pressure Tetrahedral Amorphous Carbon Synthesized by Compressing Glassy Carbon at Room Temperature
Lijie Tan, H. W. Sheng, Hongbo Lou, Benyuan Cheng, Yuanyuan Xuan, Vitali B. Prakapenka, Eran Greenberg, Qiaoshi Zeng, Fang Peng, Zhidan Zeng
Abstract
Tetrahedral amorphous carbon(ta-C) thin films with high sp3 fraction have extraordinary mechanical properties and wide applications. Despite intensive effort to increase the thickness of ta-C thin films in the past decades, bulk ta-C has not been achieved until date. In this study, by compressing a sp2-bonded amorphous carbon (glassy carbon) up to 93 GPa, we demonstrate that the formation of bulk ta-C is possible at high pressures and room temperature. We studied the atomic structure, stability, and mechanical properties of the ta-C synthesized under high pressure using in situ high-pressure X-ray diffraction and large-scale first-principles calculations. The high-pressure ta-C is mainly tetrahedrally bonded, with relatively large distortions in the sp3 C–C bonds. It can be preserved to approximately 8.5 GPa during pressure release, below which it transforms to disordered glassy carbon, accompanied by sp3-to-sp2 transition. Moreover, both the experiment and simulation show that the high-pressure ta-C has a high bulk modulus (363 ± 29 GPa, experimental) even comparable to diamond. These results deepen our understanding of amorphous carbon and help guide the synthesis of novel carbon materials using high pressure.