C13nuclear magnetic resonance in donor- and acceptor-type intercalation compounds

The ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ nuclear magnetic resonance was measured in pure graphite and its intercalation compounds of potassium and rubidium (donor type) and of bromine and nitric acid (acceptor type). The measurements were performed at room temperature and 77 K with the use of a Varian WL-112 cw spectrometer. The linewidth of the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ resonance was very broad and field dependent in the case of pure graphite because of its anisotropic magnetic susceptibilities. The linewidth for the donor-type compounds increased with decreasing concentration of the intercalant alkali metals and was found to be field independent. On the contrary, the linewidth for the acceptor-type compounds changed with the static field applied. These results are discussed in terms of the heterogeneous charge-distribution model. The ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ Knight shift with respect to pure graphite was very small for all intercalation compounds studied. The result strongly suggests that the electrons or holes produced by intercalation are of $p$ character in the vicinity of the carbon nuclear sites.