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Turbostratic or graphitic : that is the question

Published in Carbon (2017)

par PREVOTS Evelyne, PREVOTS Evelyne - publié le , mis à jour le

The study carried-out at CEMES has demonstrated that the crystal structure of graphenic particles can be identified by merely characterising their morphology at macro-scale, hence without needing to use other methods usually dedicated to crystal structure identification such as high resolution electron imaging or electron/X-ray diffraction.

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Graphenic particles are currently studied worldwide because they are likely to be useful for a large panel of applications. They can be synthesised by a variety of methods, and are rarely made of a single graphene but by several graphenes piling up instead, whole number and structural quality largely depend on the synthesis method. When subjected to flexural mechanical stresses, for instance during handling or transfer (in solution, or aerosol,…) graphenic particles respond differently, although the graphenes involved may be similar regarding their number and quality. One behaviour resembles that of a sheet of paper being folded (as in Figure a), another resembles that of a sheet of paper being crumpled (as in Figure b).

Researchers from two CNRS laboratories (CEMES in Toulouse, and CRPP in Bordeaux) have shown that this distinctive behaviour is only governed by the way graphenes superimpose in the particles, i.e., not by the presence of defects. Indeed, a graphene is built from carbon atoms displayed according to a hexagonal network, thereby constituting a periodic lattice. Depending on the history (synthesis procedure, post-treatments) which has resulted in the formation of the graphenic particles, the constituting graphenes can pile up in a manner that their respective lattices are coincidentally oriented : this is the case in genuine graphite, in which graphene stacking type and crystallographic structure are therefore both designated as "graphitic". But graphenes can also pile up randomly, i.e. according to a rotational disorder which makes that the respective lattices are no longer coincidental : the resulting stacking sequence is said "turbostratic". In the former case (graphitic), the ordered stacking sequence generates preferred bending directions corresponding to specific crystallographic direction, whereas, in the latter case (turbostratic), the random stacking sequence cannot do so.

Thanks to this relationship, it is now possible to predict which graphenic particle exhibit either a graphitic structure (case of Figure a) or a turbostratic structure (case of Figure b) by merely considering the overall morphology of graphene particles at micro-scale, without having to use any other methods specifically dedicated to structure identification such as high resolution electron imaging or electron/X-ray diffraction.

 

Reference

Monthioux M., Noé L., Kobylko M., Wang Y., Cazarès-Huerta M., Pénicaud A. Determining the structure of graphene-based flakes from their morphotype. Carbon 115 (2017) 128-133.

 

Contact

Marc Monthioux