Intercalant Concentration Research Articles

Intralayer crystal structure and order-disorder transformations of graphite intercalation compounds using electron diffraction techniques

We have used electron diffraction through the c-face to study the intercalate ordering of graphite-alkali metals (K, Rb, Cs) and graphite-halogens (Br 2, IBr, ICl). Order-disorder transformations for the in-plane structure of alkali metal and halogen intercalates have been observed by the vanishing of all superlattice diffraction spots as the sample temperature is raised. Variations of the electron diffraction patterns and of the order-disorder transformation temperatures with the intercalate species are reported. Compounds of various concentrations have been investigated, including the stage 1 graphite-alkali metals. Results obtained here are compared with structural information obtained by other techniques and by previous workers. The patterns for graphite-halogens are much more complicated than those for graphite-alkali metals. Of significance is the observation that the superlattice patterns are relatively insensitive to the intercalate concentration for compounds more dilute than stage 2 and are similar for lamellar and residue compounds. Additional superlattice patterns are observed in graphite-Br 2 below 194 °C and are similar in appearance to charge-density wave superlattice patterns reported for 2H-TaSe 2.

Magneto-optical studies of graphite intercalation compounds

High field magnetoreflection measurements are reported on the first observation of interband Landau level transitions in residue and lamellar compounds of graphite intercalated with the halogens Br 2, IBr and ICl. These magnetoreflection spectra are interpreted to yield a model for the magnetic energy level structure of these intercalation compounds in the dilute limit corresponding to stage ≳5. In this dilute limit, the insensitivity of the magnetoreflection resonances to intercalate concentration shows that near the Fermi level for pure graphite the electronic structure of the intercalation compounds is essentially independent of intercalate concentration. This conclusion results from analysis of both infrared and far-infrared magnetoreflection spectra for Landau level transitions within ±0.1 eV of the graphite Fermi level. The model for the electronic structure deduced from the magnetoreflection spectra is supported by Raman scattering results presented for the in-plane lattice modes of carbon atoms in the graphitic layer planes.

A simple model of the a-axis conductivity in graphite intercalation compounds

A simple calculation, based on the effective mass approximation and assuming a purely two-dimensional Fermi surface, is performed to estimate the dependence of a-axis conductivity σ a upon intercalant concentration X in the lamellar compounds of graphite. The predicted behavior σ a ~ X 1 2 is in approximate agreement with experiment only for the case of ICI, which is attributed to the unusually large layer spacing, hence weak interaction between layers, in this compound.

559. Rectification at the metal-selenium interface: H P D Lanyon and R E Richardson, Phys Stat Sol (a), 7 (2), Oct 1971, 411–419

We calculate the high-field and low-field in-plane magnetic susceptibilities of the transition metal chloride graphite intercalation compounds (GIC) whose spins are confined to the plane. We show that the two observed low temperature susceptibility peaks can be due to a single phase transition which occurs near the higher temperature peak. The model assumes superferromagnetism, intra-plane and inter-plane super-moment interactions, and plane to plane variations of the intercalant concentration. The parameters which we introduce are estimated for several compounds. The resultant susceptibility curves have the observed temperature and field dependences and many other formerly peculiar aspects of the magnetism are explained. Notibly, the exceptionally large magnitude of the measured susceptibility, the non-zero sample magnitization between the two susceptibility peaks, and the stage dependence of the susceptibility curves.