Pfaff, T.; Badaczewski, F.M.; Loeh, M.O.; Franz, A.; Hoffmann, J.-U.; Reehuis, M.; Zeier, W.G.; Smarsly, B.M.: Comparative Microstructural Analysis of Nongraphitic Carbons by Wide-Angle X-ray and Neutron Scattering. The Journal of Physical Chemistry C 123 (2019), p. 20532-20546
10.1021/acs.jpcc.9b03590
Abstract:
Non-graphitic carbons (NGCs) represent the most abundant class of sp2-hybridized carbon, materials (coal char coal, activated carbon, etc.). These carbons consist of small graphene layer stacks possessing significant structural disorder in both the single graphene sheets and the stacking. In this study an advanced evaluation approach for wide-angle neutron scattering (WANS) was developed, based on the method introduced by Ruland and Smarsly in 2002. In particular, we elucidated if and how the enhanced WANS data quality and larger values of the modulus of the scattering vector s-range affect the accuracy and the values of the size and disorder parameters-being fitting parameters by themselves-in comparison to wide-angle X-ray scattering (WAXS), which is usually performed by laboratory equipment. We find a reasonable agreement for the parameters La and Lc, that is, the lateral dimension and stack height, within the error bars, whereas for the disorder parameters different results for WAXS and WANS were found, the origin of which is discussed. Thus, this study addresses the general issue of how reliably microstructural parameters can be determined from WAXS/WANS by fitting simulated WAXS and WANS curves, which are quality-impaired by added Gaussian noise at different levels and cut-off at different s-values. From this analysis, we estimated the minimal data quality required for a reliable NGC microstructural analysis based on WAXS/WANS. As an important finding, these simulations show that typical, standard WAXS laboratory setups are sufficient to provide reliable values for the most relevant structural parameters. Furthermore, pairdistribution function (PDF) analyses were performed on WAXS data obtained from a synchrotron facility. Comparing PDF and WAXS/WANS fitting analysis suggests the presence of small highly ordered oligoaromatic domains embedded in the larger graphene sheets, questioning the classical view on the NGC microstructure.