Scale-dependent pathways of the graphite-to-diamond transition

The transformation from graphite to diamond is a paradigmatic pressure-induced structural phase transition in solids with fundamental insights in condensed matter physics, geoscience, and materials science. However, the atomistic pathway remains a subject of longstanding debate due to the challenge in observing the ultrafast nucleation process. To overcome the limitations of traditional high-pressure and high-temperature (HPHT) experiments, which rely on post-mortem analyses that obscure early-stage dynamics, here we combine metadynamics simulations with HPHT synthesis using dimensionally distinct carbon precursors to elucidate the microscopic nucleation and growth mechanisms. Our simulations reveal scale-dependent transformation pathways in which fluctuations in interlayer bonding precede the formation of persistent sp3-bonded diamond-like nuclei. Experimentally, by exploiting the radial confinement of multi-walled carbon nanotubes to suppress growth kinetics, we successfully capture the elusive nucleation stage, identifying 2–6 nm diamond nuclei. Using highly oriented pyrolytic graphite, we demonstrate a temperature-driven shift from interlayer to intralayer growth, which subsequently governs the genesis of twin boundaries and hexagonal diamond lamellae during final grain coalescence. These findings not only reconcile disparate theoretical models regarding the kinetic pathway but also establish a robust, precursor-mediated framework for the microstructural design of high-performance diamond materials. The study uncovers a scale-dependent graphite to-diamond pathway, showing that interlayer bonding fluctuations precede nucleation and precursor confinement captures nanoscale nuclei and regulates growth, providing a unified view of this transition.