Modifying materials by intercalation

For the past decade, materials research has focused on synthesizing new materials and generating new structural arrangements that exhibit specific desired properties. Some of the greatest advances in this area have come out of work on intercalation compounds, which are formed by the insertion of atomic or molecular layers of a guest chemical species—an intercalant—between layers in a host material. Figure 1 illustrates the basic structure of intercalation compounds. Part a of the figure depicts graphite intercalated with lithium; this structure is described as “commensurate,” because the atoms in each layer of guest material are in registry with those in the neighboring layers of the host material. Part b of the figure shows the incommensurate nature of graphite intercalated with ferric chloride. Although graphite intercalation compounds have been synthesized for over 150 years, it is only very recently that methods have been perfected to the point that one can prepare materials with specific structures and properties. These advances in materials synthesis, coupled with current theoretical interest in two‐dimensional physics, have contributed to the current high level of interest in graphite intercalation compounds.