Graphite to diamond: 2–6 nm nuclei captured in experiment

Researchers from Jilin University, Qufu Normal University and Zhejiang University have described the atomistic pathway by which graphite transforms into diamond under pressure. The results are published in Nature Communications. The team combined metadynamics simulations with high-pressure, high-temperature (HPHT) synthesis, using carbon precursors of different dimensionality doi.org.

The graphite-to-diamond transition is a standard example of a pressure-induced structural phase transition in solids, relevant to condensed matter physics, geoscience and materials science. Its atomistic pathway has been debated for a long time, because the nucleation process is ultrafast and difficult to observe. According to the authors, traditional HPHT experiments rely on post-mortem analysis, which obscures early-stage dynamics doi.org.

Simulations: scale-dependent pathways

The simulations reveal transformation pathways that depend on scale. In them, fluctuations in interlayer bonding precede the formation of persistent sp3-bonded, diamond-like nuclei doi.org.

The authors report that these findings reconcile disparate theoretical models of the kinetic pathway doi.org.

Experiments: nuclei, twin boundaries and hexagonal diamond

In the experimental part, the team used multi-walled carbon nanotubes. Their radial confinement suppresses growth kinetics, which allowed the group to capture the nucleation stage. Diamond nuclei of 2–6 nm were identified in these samples doi.org.

A second series of experiments used highly oriented pyrolytic graphite as the precursor. Here the authors observed a temperature-driven shift from interlayer to intralayer growth. According to the study, this shift governs the formation of twin boundaries and of hexagonal diamond lamellae during the final coalescence of grains doi.org.

The authors describe the work as a precursor-mediated framework for the microstructural design of high-performance diamond materials doi.org. The conclusions rest on metadynamics simulations and laboratory HPHT synthesis, with the choice of precursor, from nanotubes to oriented graphite, determining which stage of the transition could be examined doi.org.

Jilin University team captures 2–6 nm diamond nuclei in the graphite-to-diamond transition

Simulations: scale-dependent pathways

Experiments: nuclei, twin boundaries and hexagonal diamond

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