Structural studies of graphite intercalation compounds

Electron diffraction through the c-face (layer planes) and scanning electron microscopy (SEM) on the a-face (perpendicular to the layer planes) have been used to study the intralayer crystal structure and the micro-structure of graphite and its intercalation compounds. With the electron diffraction technique, the intra-layer intercalate ordering and the associated order-disorder transformations have been studied in graphitealkali metals (K, Rb, Cs) and graphite-halogens Br₂, IBr, ICl). Reported here is the first observation of order-disorder transformations in the graphite-halogen compounds. Direct evidence is given for the presence of intralayer intercalate ordering in even extremely dilute lamellar and residue compounds. Also presented here is a new a-face surface preparation technique, which involves mechanical polishing and back-sputtering. SEM observations of the a-faces reveal large microstructural differences between highly-oriented pyrolytic graphite, chemically-separated single-crystal graphite and mechanically-separated single-crystal graphite. Significant exfoliation along the c-direction occurs upon intercalation. Evidence is given for the preferential trapping of intercalate at defects in both lamellar and residue compounds.