北京大学侯仰龙团队报道了六方金刚石形成的关键理论和实验研究。相关研究成果发表在2025年1月6日出版的国际学术期刊《美国化学会杂志》。

六方金刚石（HD）于60年前被报道，因其超高的理论硬度而引起了广泛关注，比立方晶系金刚石高出58%。然而，迄今为止，由于对其形成机制的理解有限，在高压高温下合成纯HD仍然不成功。

该文中，研究人员采用系统的分子动力学模拟，直接观察了成核生长机制中石墨到HD的转变。具体而言，HD是在准单轴压缩下形成的，在石墨基面很少滑动的温和温度条件下，沿石墨的[001]方向具有较高的应力，而立方金刚石（CD）是在石墨的AB层堆叠结构被破坏，和/或在较高温度下自由滑动时形成的。

该理论工作得到了受控高温高压实验的很好证实，其中HD是在[001]g方向上具有高应力的准单轴条件下成功合成的，而CD是在AB层堆叠受到平行于基板的较高压应力干扰时合成的。

研究工作不仅阐明了石墨到金刚石转变的压力-温度控制机制，而且通过将石墨基面（001）保持在AB堆叠结构中，并精确控制基层滑动，指导了一种合成HD的新方法。

附：英文原文

Title: Key for Hexagonal Diamond Formation: Theoretical and Experimental Study

Author: Sheng-Cai Zhu, Gu-Wen Chen, Xiao-Hong Yuan, Yong Cheng, Ming-Hao Wan, Baoyin Xu, Ming-sheng Wang, Hu Tang, Yanglong Hou

Issue&Volume: January 6, 2025

Abstract: Hexagonal diamond (HD) was reported 60 years ago and has attracted extensive attention owing to its ultrahigh theoretical hardness, 58% superior to its cubic counterpart. However, to date, synthesizing pure HD under high-pressure and high-temperature (HPHT) remains unsuccessful due to the limitations of understanding the formation mechanism. In this work, employing a systematic molecular dynamics simulation, we directly observe the graphite-to-HD transition in a nucleation-growth mechanism. Specifically, HD is formed under quasi-uniaxial compression with higher stress along the [001] direction of graphite and mild-temperature conditions for the scarce sliding of the graphite basal plane, while cubic diamond (CD) is formed when the AB-layer stacking structure of graphite is destroyed and/or freely sliding under a higher temperature. Our theoretic work is well confirmed by the controlled HPHT experiment, where HD was successfully synthesized under quasi-uniaxial conditions with high stress in the [001]g direction, while CD was synthesized when AB-layer stacking was disturbed by higher compressive stress parallel to the basal sheets. Our work not only clarifies the pressure–temperature-controlled mechanisms of graphite-to-diamond transitions but also guides a novel approach to synthesize HD by maintaining the graphite basal plane (001) in an AB-stacking configuration and precisely controlling the basal layer sliding.

DOI: 10.1021/jacs.4c16312

Source: https://pubs.acs.org/doi/abs/10.1021/jacs.4c16312