Preparation of superhard, transparent carbon crystals by cold compressing graphite. (a) Hydrostatic XRD patterns for graphite compressed at ambient temperature. The inset image shows the phase transition from graphite to M-carbon. Adapted with permission from ref. [31]. Copyright 2003 American Association for the Advancement of Science. (b) XRD pattern obtained after compressing graphite to ∼50 GPa compared with the calculated results of several new carbon structures, in addition to cubic and hexagonal diamond. Adapted with permission from ref. [158]. Copyright 2012 Springer Nature. (c) High-resolution TEM and corresponding fast Fourier transform (inset) images of lonsdaleite. Adapted with permission from ref. [162]. Copyright 2016 Inderscience Enterprises Ltd. (d, e) XRD patterns of compressed and sheared graphite (d) at 0.4 GPa with 45° anvil rotation and (e) after quenching to room pressure from 0.7 GPa. (f) High-resolution TEM and fast Fourier transforms (inset) of an orthorhombic structure. Adapted with permission from ref. [163]. Copyright 2019 Elsevier.