CESR of lamellar compounds of graphite with alkali metals: A study comparing pyrographite and graphite fibers

Abstract

The conduction electron spin resonance (CESR) of interculated compounds of graphite with potassium (stages 1 – 4) and lithium (stages 1 – 2) has been investigated using, as host materials, pyrographite (HOPG) and a graphite fiber based on a mesophase pitch (both from Union Carbide). The EPR characteristics, linewidth, lineshape and, g-factor, have been measured between 5 and 300 K on the different samples. The theory of the spin-lattice relaxation for classical metals has been used to explain these results. The electron-phonon interaction and the influence of defects on the charge carriers are considered to interpret the linewidth values and their temperature dependences. However, a specific behavior at low temperature ( T < 100 K) has been found. The intercalation compounds of graphite with either donors or acceptors constitute a group of materials amongst the synthetic metals of restricted electronic dimensionality. With alkali metals a series of well-defined stoichiometric stages can be prepared [1]: they present an ideal class of compounds with which to carry out a systematic investigation in order to find the general trends for a given intercalant.