Electron-diffraction study of rubidium-intercalated graphite.

Abstract

Using an analytical scanning transmission electron microscope we monitored the in-plane structure of rubidium-intercalated graphite as it underwent the deintercalation process. Starting with a saturated, stage-1 sample and using a temperature-controlled sample stage to control the desorption process, we allowed the graphite to deintercalate over a period of many days. This created a series of unannealed structures of progressively higher stage number. The experiment encompassed a regime in which the dominant factor in determining the intercalant in-plane distribution changed from host-intercalant to intercalant-intercalant interactions. High-resolution electron diffraction techniques were used to follow the in-plane superlattice structure of the intercalant. Ordered commensurate superlattices were observed which were stable over the entire temperature range observed (79--300 K) . In addition, an amorphous phase was observed which underwent a phase transition to an incommensurate square array. Both commensurate and incommensurate transition structures were observed during the transition period. The incommensurate structure was not affected by temperature and does not match the general lattice parameters for incommen- surate lattices which have been previously reported in the alkali-metal-intercalated graphite compounds.