Detonation-induced transformation of graphite to hexagonal diamond

TL;DR

This study investigates how shock waves transform graphite into hexagonal diamond using in-situ X-ray diffraction and computational methods, revealing conditions favoring hexagonal diamond formation without cubic diamond appearance.

Contribution

It provides experimental evidence of hexagonal diamond formation under shock and theoretical insights into the transition energy barriers, advancing understanding of high-pressure carbon phases.

Findings

Hexagonal diamond forms above 50 GPa during shock.

Uniaxial compression lowers the energy barrier for hexagonal diamond.

No cubic diamond observed up to 70 GPa.

Abstract

We explore the structural evolution of highly oriented pyrolytic graphite (HOPG) under detonation-induced shock conditions using in-situ synchrotron X-ray diffraction in the ns time scale. We observe the formation of hexagonal diamond (lonsdaleite) at pressures above 50 GPa, in qualitative agreement with recent gas gun experiments. First-principles density functional calculations reveal that under uniaxial compression the energy barrier for the transition towards hexagonal diamond is lower than cubic diamond. Finally, no indication of cubic diamond formation was observed up to >70 GPa.