石墨向金刚石转变中的晶界介导动力学阻滞
Grain-boundary-mediated kinetic arrest in graphite-to-diamond transformation
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中文总结 AI 辅助
研究石墨向金刚石转变在HPHT下的变异性，通过分子动力学模拟发现前驱体晶粒结构控制转变途径，晶界影响成核与生长，确定结构异质性为控制参数，前驱体结晶度可调控转变途径。
中文摘要 AI 辅助
在高压高温（HPHT）条件下，石墨向金刚石的转变表现出显著的变异性，尽管合成条件相似，却会产生金刚石、石墨相或亚稳态的金刚石 - 石墨混合纳米复合材料。现有的原子模型大多基于理想化的单晶石墨，无法解释HPHT条件下部分转变中间态的持续性。本文通过大规模分子动力学模拟表明，前驱体晶粒结构通过将金刚石成核与协同转变传播解耦来控制石墨向金刚石的转变途径。晶界首先促进局部sp³成核，之后金刚石在单个晶粒内生长，但在晶体学不匹配的晶界处受阻。结果，结构异质的石墨稳定了动力学阻滞的混合sp² - sp³态，而大尺寸或单晶域有利于协同整体转变为金刚石。我们的发现将结构异质性确定为压力和温度之外缺失的控制参数，将亚稳态转变产物重新定义为由前驱体微观结构产生的动力学捕获态，而非热力学中间体。因此，前驱体结晶度成为控制石墨向金刚石转变途径的实际控制参数。
英文摘要
The graphite-to-diamond transition exhibits striking variability under high-pressure, high-temperature (HPHT) conditions, producing diamond, graphitic phases, or metastable, mixed diamond-graphite nanocomposites despite similar synthesis conditions. Existing atomistic models, largely based on idealised single-crystal graphite, do not explain the persistence of partially transformed intermediate states under HPHT conditions. Here, using large-scale molecular dynamics simulations, we show that precursor grain structure governs graphite-to-diamond transformation pathways by decoupling diamond nucleation from cooperative transformation propagation. Grain boundaries first facilitate local sp$^3$ nucleation, after which diamond growth propagates within individual grains but becomes arrested at crystallographically mismatched grain boundaries. As a result, structurally heterogeneous graphite stabilizes kinetically arrested mixed sp$^2$-sp$^3$ states, whereas large or single-crystalline domains favour cooperative bulk transformation into diamond. Our findings identify structural heterogeneity as a missing control parameter alongside pressure and temperature, reframing metastable transformation products as kinetically trapped states arising from precursor microstructure rather than thermodynamic intermediates. Precursor crystallinity therefore emerges as a practical control parameter governing graphite-to-diamond transformation pathways.
