Modeling of disorder and X-ray diffraction in coal-based graphitic carbons Original Research Article

In this work, X-ray diffractograms of about 20 coal-based graphites and carbons, with different degrees of graphitic order, have been modeled using the recent computational model of Shi et al. This model relates the crystalline parameters c (2d002) and a and the crystallite sizes Lc and La, to the parameters of the disorder present in carbons. These disorder parameters include the probability P for a random displacement δ between adjacent layers, the probability Pt for finding a 3R stacking fault, the strain parameters, and the preferred orientation. Plots among d002, Lc, and La lead us to conclude that a step transition exists in graphites near d002- = 3.37 Å where a two-fold increase in Lc is observed for a fixed La. This observation of a step at 3.37 Å is consistent with the recent observation of Bragg et al. in a graphite where disorder was produced by successive grinding, thermal treatments and neutron irradiation. A theoretical interpretation of this step-transition is however not yet available. Plots of d002 against 〈δ2〉, 2P, (2P + Pt) are discussed in terms of the disorder models proposed by Franklin and by Ruland. The preferred orientation evaluated from the fit varies systematically with the ratio LcLa and the experimental X-ray anisotropy ratio.