Theoretical study on phase transition of various graphitic structures under high pressure

• Published in: Diamond and related materials 2023-03, Vol.133, p.109725, Article 109725
• Main Authors: Han, Qiaoyi, Luo, Kun, Gao, Qi, Wu, Yingju, He, Julong
• Format: Article
• Language: English
• Subjects: Diamond polytypes; First-principles calculations; Phase transition
• ISSN: 0925-9635; 1879-0062
• DOI: 10.1016/j.diamond.2023.109725

Recently, the structural fragments of the 2H, 4H, 9R, and 15R diamond polytypes were found in the synthesized diamond crystals by high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM). This work mainly uses onion carbon as a raw material, a complex layered structure, thus attracting us to focus on the influence of precursor structure on the formation of diamond polytypes. Herein, we selected nine graphitic structures with different stacking sequences from previous work to study their phase transition under different compression methods using DFT (density functional theory) calculations. Most of them appeared as interlayer slips during compression and finally produced 3C, 2H, and 9R diamond polytypes. The hexagonal character unit (h) was derived only from the initial AA stacking layer in the graphite precursor after analyzing the phase transition process. Meanwhile, the design of a suitable preparation scheme that maximizes the retention of stacking faults from the precursor into the product is the key to the synthesis of non-3C(cubic) diamonds. Thus, this study provides insights into the high-pressure transformation of graphite systems with diverse structures and illustrates the reasons why non-3C diamonds are rare. [Display omitted] •Nine graphitic structures were selected to study their phase transition.•The AAB graphitic structure can transform into a 9R polytype or 3C diamond.•AA stacking and ultra-fast pressurization will contribute to synthetize polytypes.