Structural transitions in the graphite-AlCl 3-FeCl 3 system

Abstract

X-ray, electron diffraction and electron energy loss spectroscopy reveal the transition process of the stage and basal-plane structures in the graphite-AlCl 3-FeCl 3 system reaction between stage-2 FeCl 3-GMIC (graphite monointercalation compound) and gaseous aluminum(III) chloride (AlCl 3). The intercalant iron(III) chloride (FeCl 3) is replaced by the intercalated AlCl 3 even at 150°C, and finally the FeCl 3-GMIC changes into stage-1 AlCl 3-GMIC. In the intermediate stage of this process, the synthesized compound has an alternative stacking of the intercalant FeCl 3 and AlCl 3, layers, which corresponds to the stage structure of AlCl 3-FeCl 3-GBIC (graphite biintercalation compound). In this transition process, the basal-plane structure of intercalant FeCl 3 maintains its original structure until the intercalant FeCl 3 deintercalates completely. As for the intercalant AlCl 3, the basal-plane structure of the microcrystalline state appears in the early stage of this reaction. The microcrystals expand the galleries between graphite layers as pillars, so that the repeat distance of the compound is the same as that of GBIC even if the concentration of the intercalant AlCl 3 is low. The structure of the microcrystal turns into the rectangular structure with a well-defined orientation to graphite lattice as the intercalation of AlCl 3 proceeds. These basal-plane structures of the intercalant AlCl 3 can also be observed in AlCl 3-GMIC. The GBIC is not homogeneous on the micrometer scale. The cause of deintercalation of FeCl 3 is discussed from the viewpoint of AlFeCl 6 complex formation.