Synthetic metals based on graphite/aluminium halides

Abstract

Halides that are active Friedel Craft catalysts with aromatic compounds have been used to prepare synthetic metals. Aluminium bromide AlBr 3 intercalates readily into well oriented graphite between 70 and 80 °C. Second stage intercalation compounds are formed with approximate composition (C 33 AlBr 3.6 ). Aluminium chloride AlCl 3 does not intercalate spontaneously to any appreciable extent, unless free chlorine is also present. In this case, intercalation begins at about 60 °C and reaches a limit after several hours between 70 and 80 °C to produce a first stage intercalate with approximate composition (C 18 + AlCl 4 - .AlCl 3 ). In the direction of the a -axes both halide intercalates show good metallic conductivity with p characteristics. Unlike the parent graphite, temperature coefficients of resistivity of these synthetic metals are comparable with those of natural metals, indicating that thermal vibrations of charged atoms or molecules in the crystal compound contribute a dominant scattering mechanism controlling the electrical conductivity.