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.
@article{arxiv.2007.11225,
title = {Detonation-induced transformation of graphite to hexagonal diamond},
author = {Elissaios Stavrou and Michael Bagge-Hansen and Joshua A. Hammons and Michael H. Nielsen and Bradley A. Steele and Penghao Xiao and Matthew P. Kroonblawd and Matthew D. Nelms and William L. Shaw and Will Bassett and Sorin Bastea and Lisa M. Lauderbach and Ralph L. Hodgin and Nicholas A. Perez-Marty and Saransh Singh and Pinaki Das and Yuelin Li and Adam Schuman and Nicholas Sinclair and Kamel Fezzaa and Alex Deriy and Lara D. Leininger and Trevor M. Willey},
journal= {arXiv preprint arXiv:2007.11225},
year = {2020}
}