We develop a picture of graphenic crystallites within disordered carbons that
goes beyond the traditional model of graphitic platelets at random orientation.
Using large atomistic models containing one million atoms, we redefine the
meaning of the quantity La extracted from X-ray diffraction (XRD) patterns. Two
complementary approaches are used to measure the size of graphenic
crystallites, which are defined as regions of regularly arranged hexagons.
Firstly, we calculate the X-ray diffraction pattern directly from the atomistic
coordinates of the structure and analyse them following a typical experimental
process. Second, the graphenic crystallites are identified from a direct
geometrical approach. By mapping the structure directly, we replace the
idealised picture of the crystallite with a more realistic representation of
the material and provide a well-defined interpretation for La​ measurements
of disordered carbon. A key insight is that the size distribution is skewed
heavily towards small fragments, with more than 75% of crystallites smaller
than half of La​