No abstract

An ordering transition at 155 K is reported for the stage 2 InCl3 graphite intercalation compound. It was detected as a sharp decrease in the resistivity during the first cooling of a sample. It was observed also by differential thermal analysis during both warming and cooling. X-ray diffraction from intercalated single crystals showed an ordered phase at room temperature after a sample was cooled below the transition temperature. The ordered phase has a (4 square root 3*4 square root 3)R30 degrees unit cell with respect to the hexagonal graphite lattice.

Perylene (Per) was reacted with , and in solid-solution reactions to produce solvent-free , and . X-ray diffraction identified the unit cells of the compounds as being orthorhombic in the first two cases and tetragonal in the last case. All of the compounds exhibited an increase in resistance with decreasing temperature indicative of a semiconducting type of behaviour and had room temperature resistivities of , , and , respectively. The conduction process has been analysed by fitting the data with a number of parameters in order to account for a nonlinearity in the versus 1/T curves. The polaronic hopping model employed includes contributions of multiphonon processes, and intragrain and intergrain effects, and provides a good fit to the resistivity data as well as consistency with the results of Hall effect measurements.

The de Haas-van Alphen ͑dHvA͒ effect of the stage-2 InCl 3 graphite intercalation compound was studied with two dHvA spectrometers, one providing fields up to 14 T and temperatures between 50 and 800 mK and the other up to 5.5 T in the temperature range 1.5-4.2 K. Fifteen dHvA frequencies were measured along with the cyclotron masses of many of them. The frequencies were explained by the zone folding of the two Fermi-surface cylinders of the stage-2 compound. The orbits were formed by translation of the 8ͱ3 ϫ8ͱ3R30°lattice of the intercalant molecules.

The stage-1 InCl 3 graphite intercalation compound (GIC) was studied by the de Haas-van Alphen (dHvA) effect in the temperature range 1.4 to 4.2 K with magnetic fields from 3 to 5 T. The observed dHvA oscillations possess frequencies of f 1 = 263 T, f 2 = 458 T, f 3 = 705 T and f 4 = 878 T. They are shown to result from Fermi surface pieces which are constructed from the zone folding of the two-dimensional free electron Fermi surface. The fragmentation of the Fermi surface is shown to be a consequence of the additional periodicity of a commensurate (8• in-plane superlattice formed by the InCl 3 molecules. This ordering of InCl 3 molecules is a result of a phase transition which occurs upon cooling at approximately 260 K. This transition was identified by temperature dependent resistivity studies and by differential thermal analysis (DTA) of the stage-1 InCl 3 GIC sample.