Structural studies of disordered carbons by high-energy X-ray diffraction

X-ray diffraction measurements were carried out on three samples of disordered, commercially produced carbons, AX21, CXV and BP71, on the ID15B beam-line at the European Synchrotron Radiation Facility (ESRF), Grenoble. Intensity data were converted to pair correlation functions via the Fourier transform. The results obtained show that the structure of the studied samples consists of one four graphite-like layers, stacked without spatial correlations. The size of the ordered regions is in the range of 9-16 angstrom. The atomic arrangement within an individual layer can be described in terms of the paracrystalline ordering, in which lattice distortions propagate proportionally to the square root of interatomic distances. The paracrystalline structure was simulated by introducing the Stone Wales defects (pair of two pentagons and two heptagons), randomly distributed in the network. The resulting structures were relaxed using the reactive empirical bond order potential for carbon-carbon interaction and the Lennard-Jones potential with parameters for interlayer interactions. Such defects lead to curvature of individual layers.