Nat Mater. 2011 Jul 24;10(9):693-7. doi: 10.1038/nmat3078.
Graphite and diamond have comparable free energies, yet forming diamond from graphite in the absence of a catalyst requires pressures that are significantly higher than those at equilibrium coexistence. At lower temperatures, the formation of the metastable hexagonal polymorph of diamond is favoured instead of the more stable cubic diamond. These phenomena cannot be explained by the concerted mechanism suggested in previous theoretical studies. Using an ab initio quality neural-network potential, we carried out a large-scale study of the graphite-to-diamond transition assuming that it occurs through nucleation. The nucleation mechanism accounts for the observed phenomenology and reveals its microscopic origins. We demonstrate that the large lattice distortions that accompany the formation of diamond nuclei inhibit the phase transition at low pressure, and direct it towards the hexagonal diamond phase at higher pressure. The proposed nucleation mechanism should improve our understanding of structural transformations in a wide range of carbon-based materials.
石墨和金刚石的自由能相当，但在没有催化剂的情况下将石墨转化为金刚石所需的压力远高于平衡共存时的压力。在较低的温度下，更稳定的立方金刚石反而会形成亚稳态的六方金刚石多晶型。这些现象不能用之前理论研究中提出的协同机制来解释。我们使用基于第一性原理的高质量神经网络势，对假定通过成核发生的石墨到金刚石的转变进行了大规模研究。成核机制解释了所观察到的现象，并揭示了其微观起源。我们证明，伴随金刚石核形成的大晶格畸变会抑制低压下的相变，并使其在更高压力下向六方金刚石相转变。所提出的成核机制应能增进我们对广泛的含碳材料中结构转变的理解。
