Shear Assisted Diamond Formation in Cold-Compressed HOPG

Abstract

Diamond synthesis from a graphite precursor is primarily constrained by the requirement for the simultaneous application of extreme pressures and temperatures. We explore the microstructural changes in highly oriented pyrolytic graphite subject to shear during room temperature compression. Using a diamond anvil cell, nonhydrostatic pressures of up to 160 GPa were applied, resulting in an optically transparent, diamond-like material above 80 GPa that reverted to an opaque, largely graphite-like material upon decompression. Detailed microstructural analysis of the recovered sample revealed nanoscale diamond-like domains embedded within a graphitic matrix containing shear bands and localized basal slip features consistent with a high shear environment. Employing a rotational diamond anvil cell greatly enhanced these shear-induced features, producing significant amounts of diamond in samples recovered from applied pressures as low as 15 GPa. These findings demonstrate that shear can facilitate the graphite-to-diamond transformation, enabling sp3 bond formation under conditions where extreme temperatures are not required.