Nuclear Magnetic Resonance Study of Fluorine-Graphite Intercalation Compounds

To study the origin of semimetal-metal and metal-insulator transformations, localization effects and C-E bonding in fluorine-intercalated graphite CxF, 13C and 19F NMR investigations have been carried out for a wide range of fluorine content, 3.8 < x < 12.7. Fluorine spectra for small fluorine content, x > 8, are attributed to mobile fluorine acceptor species which are responsible for the increase of electric conductivity in the dilute compound. When increasing the fluorine content to x ∼ 8 corresponding to the maximum electric conductivity, covalent C-P bonds start to oc- cur. The number of these bonds grows with fluorine content resulting in the decrease in conductivity which is caused by a percolation mechanism rather than by a change in bond length. A difference in 19F chemical shift for fluorine-intercalated graphite CxF and covalent graphite fluoride (CF)n has been observed and is attributed to different C-P bonding in these compounds