The Transformation\nMechanism of Graphite to Hexagonal\nDiamond under Shock Conditions

The formation of a hexagonal diamond represents one of\nthe most\nintriguing questions in materials science. Under shock conditions,\nthe graphite basal plane tends to slide and pucker to form diamond.\nHowever, how the shock strength determines the phase selectivity remains\nunclear. In this work, using a DFT-trained carbon global neural network\nmodel, we studied the shock-induced graphite transition. The poor\nsliding caused by scarce sliding time under high-strength shock leads\nto metastable hexagonal diamond with an orientation relationship of\n(001)<sub>G</sub>//(100)<sub>HD</sub>+[010]<sub>G</sub>//[010]<sub>HD</sub>, while under low-strength shock due to long sliding distance\ncubic diamond forms with the orientation (001)<sub>G</sub>//(111)<sub>CD</sub>+[100]<sub>G</sub>//[110]<sub>CD</sub>, unveiling the strength-dependent\ngraphite transition mechanism. We for the first time provide computational\nevidence of the strength-dependent graphite transition from first-principles,\nclarifying the long-term unresolved shock-induced hexagonal diamond\nformation mechanism and the structural source of the strength-dependent\ntrend, which facilitates the hexagonal diamond synthesis via controlled\nexperiment.