No abstract

Non-graphitic carbons (NGCs), such as glass-like carbons, pitch cokes, and activated carbon consist of small graphene layer building stacks arranged in a turbostratic order. Both structure features, including the single graphene sheets as well as the stacks, possess structural disorder, which can be determined using wide-angle X-ray or neutron scattering (WAXS/WANS). Even if WANS data of NGCs have already been extensively reported and evaluated in different studies, there are still open questions with regard to their validation with WAXS, which is usually used for routine characterization. In particular, using WAXS for the damping of the atomic form factor and the limited measured range prevent the analysis of higher-ordered reflections, which are crucial for determining the stack/layer size (La, Lc) and disorder (σ1, σ3) based on the reflection widths. Therefore, in this study, powder WANS was performed on three types of carbon materials (glass-like carbon made out of a phenol-formaldehyde resin (PF-R), a mesophase pitch (MP), and a low softening-point pitch (LSPP)) using a beamline at ILL in Grenoble, providing a small wavelength and thus generating WANS data covering a large range of scattering vectors (0.052 Å−1 < s < 3.76 Å−1). Merging these WANS data with WANS data from previous studies, possessing high resolution in the small s range, on the same materials allowed us to determine both the interlayer and the interlayer structure as accurately as possible. As a main conclusion, we found that the structural disorder of the graphene layers themselves was significantly smaller than previously assumed.

We present a free software script operating in GNU Octave for the refinement of wide-angle X-ray and neutron scattering (WAXS/WANS) data of non-graphitic carbons (NGCs). The refinement script (OctCarb) is based on the evaluation approach of Ruland and Smarsly (2002). As result, up to 14 physically meaningful parameters such as the layer extension La, the stack height Lc, as well as the degree of disorder of the graphenes and their stacking are obtained through a well-established fitting routine. In addition, background scattering based on specific physical phenomena and different correction parameters such as polarization and absorption can be considered. Since the complex mathematical calculations are implemented and performed in the background, with only a few settings to be made, the software was designed to be usable by inexperienced users. As another key feature, Octave and thus OctCarb run on all common operating systems (Windows, MacOS and Linux), and can even be used on high-performance computing clusters (HPCs) to perform multiple calculations at once. In addition to this, the whole refinement can be performed within minutes, and it is possible to tweak and optimize it for special purposes and measuring geometries. These features make OctCarb useful for all scientists dealing with the characterization of NGCs by X-ray or neutron scattering techniques.