Dong Jiajun, Yao Zhen, Yao Mingguang, Li Rui, Hu Kuo, Zhu Luyao, Wang Yan, Sun Huanhuan, Sundqvist Bertil, Yang Ke, Liu Bingbing
State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China.
Institute of Materials Science and Engineering, Changchun University of Science and Technology, Changchun 130022, China.
Phys Rev Lett. 2020 Feb 14;124(6):065701. doi: 10.1103/PhysRevLett.124.065701.
Graphite is known to transform into diamond under dynamic compression or under combined high pressure and high temperature, either by a concerted mechanism or by a nucleation mechanism. However, these mechanisms fail to explain the recently reported discovery of diamond formation during ambient temperature compression combined with shear stress. Here we report a new transition pathway for graphite to diamond under compression combined with shear, based on results from both theoretical simulations and advanced experiments. In contrast to the known model for thermally activated diamond formation under pressure, the shear-induced diamond formation takes place during the decompression process via structural transitions. At a high pressure with large shear, graphite transforms into ultrastrong sp^{3} phases whose structures depend on the degree of shear stress. These metastable sp^{3} phases transform into either diamond or graphite upon decompression. Our results explain several recent experimental observations of low-temperature diamond formation. They also emphasize the importance of shear stress for diamond formation, providing new insight into the graphite-diamond transformation mechanism.
众所周知，石墨在动态压缩或在高压和高温共同作用下，通过协同机制或成核机制可转变为金刚石。然而，这些机制无法解释最近报道的在室温压缩与剪切应力共同作用下金刚石形成的发现。在此，我们基于理论模拟和先进实验的结果，报告了一种在压缩与剪切共同作用下石墨向金刚石转变的新途径。与已知的压力下热激活金刚石形成模型不同，剪切诱导的金刚石形成在减压过程中通过结构转变发生。在高压力和大剪切力作用下，石墨转变为超硬的sp³相，其结构取决于剪切应力的程度。这些亚稳的sp³相在减压时会转变为金刚石或石墨。我们的结果解释了最近几项关于低温金刚石形成的实验观察结果。它们还强调了剪切应力对金刚石形成的重要性，为石墨 - 金刚石转变机制提供了新的见解。
