IN-SITU ESR STUDY OF THE HNO3-INTERCALATE DIFFUSION PROCESS IN GRAPHITE-INTERCALATION COMPOUNDS

In situ conduction electron spin resonance (CESR), contactless conduct ivity and X-ray diffraction studies of HNO3 molecule intercalation int o highly oriented pyrolytic graphite (HOPG) plates are presented. The CESR lineshape, linewidth, intensity and position analysis allow us to establish: a) individual reaction steps, b) two different intercalati on mechanisms: a slow diffusion of the intercalate through faces paral lel to the c-axis in the whole thickness of a sample and a relatively faster nucleation of a new phase in near surface galleries; and c) an estimate of the constant of the two-dimensional diffusion of intercala te through the sample after its insertion into HOPG. Each of the inter calation mechanisms is characterized by an 'induction period', in whic h the graphite takes up comparatively little intercalate, and by an in dex of the stage appearing on its own. (C) 1997 Elsevier Science Ltd. All rights reserved.