Equilibrium and non-equilibrium effects in high pressure phase transformations of carbon

Lyu, Yanjun [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, USA]; Lindsey, Rebecca K [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, USA; Department of Chemical Engineering, University of Michigan, Ann Arbor, MI, USA]; Bastea, Sorin [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)]; Hamel, Sebastien [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)]; Lordi, Vincenzo [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)]

doi:10.1038/s43246-026-01179-w

DOE OSTI · 3685249

Equilibrium and non-equilibrium effects in high pressure phase transformations of carbon

Lyu, Yanjun [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, USA]·Lindsey, Rebecca K [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, USA; Department of Chemical Engineering, University of Michigan, Ann Arbor, MI, USA]·Bastea, Sorin [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)]·Hamel, Sebastien [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)]·Lordi, Vincenzo [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)]

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Abstract

The behavior of carbon in the range 1–100 GPa and 1–10 kK is central to problems in planetary interiors, inertial confinement fusion targets, and high-pressure synthesis of carbon-based materials, but experiments in this regime are difficult and often provide only indirect constraints on phase behavior. As a result, phase boundary loci, structure, and limits of metastability at high pressure remain uncertain. In this work, machine-learning enhanced atomistic simulations are used to address this knowledge gap. We determine the melt line up to 100 GPa, the graphite-diamond phase boundary up to the melt line, and analyze structure of the coexisting phases. We show that the coexisting liquid evolves smoothly with pressure without evidence for a first-order liquid–liquid transition. Orientation-resolved graphite melting simulations indicate that basal-plane interfaces develop a dewetting layer and undergo layer-by-layer melting, producing kinetic hysteresis and an apparent orientation dependence of the melt line. Non-equilibrium quenches from the melt are used to construct a kinetically limiting graphite–diamond phase boundary for rapid quenches from above the melt line, and show that graphite is metastable at pressures of up to ≈ 25 GPa. These results provide bounds on equilibrium and metastable behavior in carbon relevant for interpreting high-pressure experiments and for designing synthesis pathways to specific carbon microstructures.

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Lyu, Yanjun [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, USA], Lindsey, Rebecca K [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, USA; Department of Chemical Engineering, University of Michigan, Ann Arbor, MI, USA], Bastea, Sorin [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)], Hamel, Sebastien [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)], Lordi, Vincenzo [Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)]. 2026-05-20. Equilibrium and non-equilibrium effects in high pressure phase transformations of carbon. https://doi.org/10.1038/s43246-026-01179-w

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