Ammonia occlusions in graphitic cavities

Graphite intercalation compounds (GICs) with electron donors such as alkali metals, alkaline earth metals, or lanthanides, can be obtained by conversi on of graphite with solutions of the respective metal in liquid ammonia. In case of using flake graphite as the starting material for the conversion w ith Li-ammonia solutions metastable GICs are formed, whose stoichiometry de pends on the Li-concentration in the solution. Whereas such flake graphite based Li-ammonia GICs decompose slowly by expelling NH3 gas, samples based on highly oriented pyrolytic graphite (HOPG) decompose immediately after ha ving been separated from the reaction solution. The so formed residual comp ound contains only small traces of Li metal, but still some amount of NH3 g as. If the residual compound is exposed to vacuum, it expands by a factor 2 to 3. This process proved to be reversible: even after 100 expansion-contr action cycles no degradation of the material could be detected.