Structural and electronic changes in graphite fluorides as a function of fluorination rate: An XRS, PDF and DFT study

Abstract

In the present paper, graphite fluoride compounds CxF with various degrees of fluorination (x = 4, 2 and 1), i.e., with different C-F bonding characteristics, were systematically investigated using X-ray Raman Spectroscopy (XRS) and X-ray and neutron diffraction by means of Pair Distribution Function (PDF) analysis. For both techniques, ab-initio calculations allow the experimental results and structural/bonding assignments to be explained and/or confirmed. Presented here for the three stoichiometries are results for the carbon and fluorine first-neighbour distances, the evolution of the electronic band structure due to the change of the carbon hybridization upon fluorination, and also the nature of the final states for 1s core-electron excitations. Since fluorination is limited by the diffusion of fluorine in the carbon lattice, the process is less effective in the bulk, where a graphitic core remains. The cross-checked XRS, PDF data and Density Functional Theory (DFT) simulations appear also to be a powerful method to highlight the presence of a residual graphitic core, even at the highest fluorine content, in such semi-disordered and structurally complex compounds.