Alkali graphite intercalation compounds electronic structures

Carbon atoms crystallize in several forms. Graphite and diamond are well known carbon polymorphs. Fullerenes, which were discovered in the 1980 s, have also been well characterized. Carbon materials show a variety of different physical and chemical properties. Because of this the electronic structure of carbon materials has been investigated using a number of different experimental techniques, for example, XPS, UPS and XANES. Theoretical studies of carbon materials have been also performed. However, experimentally observed spectra are not always consistent with theoretical predictions. Recently, in order to understand the various kinds of observed electronic spectra, DV-Xa calculations have been performed on a small cluster model. [1] In the present paper, we report results of DV-Xa calculations performed on the carbon materials graphite, alkali graphite intercalation compounds (GIC), fullerene, and fluorinated fullerenes. 

Graphite Intercalation Compounds.— The reactions of graphitizable carbons leading to the formation of graphite intercalation compounds have been reviewed. Emphasis was placed on the insertion of alkali metals (Na), halogens (Brg), and acids (H2SO4). The effects of electronic structure and electron exchange on intercalation reactions were also considered. 

The properties of the intercalation compound, potassium graphite, KCg, have been detailed in several review articles.34/35 The bonding in potassium graphite is described in terms of the limiting structure, K+Cg", and it is believed that the anion forms as a result of the transfer of an electron from the alkali metal to the conduction band of graphite. Novikov and Volpin35 have noted a similarity between aromatic radical-anions and alkali metal-graphite intercalation compounds. Their observation was based on inspection of reduction potentials of aromatic hydrocarbons relative to biphenyl, Table 9.2 ... 

Tatar, R. C. 1985. A theoretical study of the electronic structure of binary and ternary first stage alkali intercalation compounds of graphite. PhD Thesis, University of Pennsylvania, PA. 

Alkali metals and bromine react with graphite to form solids known as intercalation compounds, where the foreign atoms are inserted between the intact graphite layers. Many other layered solids, for example dichalcogenides such as TaS2, which have structures similar to Cdl2 will also for intercalation compounds. The inserted species may be alkali metals, or electron donor molecules such as amines or organometallic compounds. 

Although there are numerous families of lamellar solids, only a handful of them exhibit the kind of versatile intercalation chemistry that forms the basis of this book. In arriving at the content of this volume, the editors have accurately identified six classes of versatile layered compounds that are at the forefront of materials intercalation chemistry, namely, smectite clays, zirconium phosphates and phos-phonates, layered double hydroxides (known informally as hydrotalcites or anionic clays ), layered manganese oxides, layered metal chalcogenides, and lamellar alkali silicates and silicic acids. Graphite and carbon nanotubes have not been included, in part because this specialty area of intercalation chemistry is limited to one or two molecular layers of comparatively small guest species that are capable of undergoing electron transfCT reactions with the host structure. 

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