19F NMR study of CF bonding and localization effects in fluorine-intercalated graphite

The CF bonding and localization effects in fluorine-intercalated graphite CxF with 3.8 ⩽ x ⩽ 6.5 have been studied by 19F NMR. An analysis of 19F shielding measured in our experiment and of data taken from the literature shows that the changing character of the CF bond occurs for x < 3 whereas the change in conductivity occurs for x in the range from 3 to 6. We suggest that the drop in conductivity for fluorine concentrations above that corresponding to σmax is caused by a percolation mechanism rather than by the change in bond length.