Microstructure analysis of non-graphitic carbons by wide-angle neutron scattering
Among the sp2 hybridized carbons the so called non-graphitic carbons (NGCs), a million-ton-scale material, are of significant relevance for applications and comprise a plurality of carbons such as activated carbon, glassy carbon, etc. Hence, a quantitative determination of the atom-scale microstructure based on experimentally accessible parameters is crucial for the understanding of the linkage between material properties and the microstructure. NGCs consist of graphene stacks typically possessing nanometre dimensions and substantial structural disorder. As major structural feature the graphene stacks possess rotational and translational disorder, a turbostratic arrangement. This absence of long-range crystallographic order causes broad and overlapping scattering maxima in wide angle X-ray and neutron scattering (WAXS, WANS).
Important microstructural parameters of the graphene stacks are La and Lc, which are the average lateral extension and the stack height. Further important parameters were introduced to quantify the substantial disorder in the stacking and the layers themselves.
The present study targets the precise determination of these parameters. Since the accuracy in the separation of size and disorder from WAXS/WANS reflections generally requires the analysis of several higher order reflections of one lattice family, WANS measurements were performed at the ILL (Grenoble), allowing for quite high values of the scattering vector modules. The samples were made from three different precursors and heat treated to different temperatures up to 3000 °C. More specifically, a resole-based glass-like carbon (PF-R, H), a mesophase pitch-based carbon (MP) and a low softening point pitch (LSPP, WP) were used to identify and understand the intrinsic disorder more specific. Two approaches were used to study the size and disorder of the graphene stacks. First, the WANS data were fitted using the approach of Ruland and Smarsly, providing the structural parameters as fitting parameters. Second, the pair-distribution function (PDF) analysis was performed on the WANS data obtained. Comparing WANS and PDF analysis provides insights into the understanding of the nature of the atomic disorder of such carbon materials. This leads to a more detailed analysis and knowledge of the relationship between the long-range and short-range disorder, which influence the macroscopic properties.
 T. Pfaff, F. Badaczewski, B. M. Smarsly et. al., J. Phys. Chem. C 2019