Phase transformations in glassy carbon under dynamic compression

Glassy carbon (g-C), also known as vitreous carbon, is a metastable, pure sp² carbon phase composed of a random assembly of twisted graphene fragments, resulting in a material with a lower density than graphite. The amorphous nature of g-C enables the exploration of novel bonding configurations and phase transitions that are challenging to observe in crystalline materials. We investigate the metastability of g-C and its transformation into diamond, as well as metastable and stable carbon liquids, across a wide range of pressures and temperatures using large-scale molecular dynamics (MD) simulations. Quantum-accurate MD simulations are made possible by employing an Atomic Cluster Expansion (ACE) machine-learning interatomic potential for carbon. Our MD shock simulations of g-C have uncovered a sequence of material transformations that can be directly compared with shock experiments at the European X-ray Free Electron Laser (EuXFEL) facility, aiding in the interpretation of X-ray diffraction measurements of g-C’s structural evolution.