ESR study of dilute intercalation compounds: C/F, C/K/F and C/Li/F

The intercalation of fluorine into HOPG is a relatively slow process and enables one to study quasiequilibrium states during the intercalation process. A very interesting ESR spectrum is observed at the initial intercalation process. The room temperature spectrum consists of several new lines at g = 2.002 ± 0.002 (line 'a') and g = 2.015 ± 0.002 (line 'b'). Line 'b' and possibly line 'a' (at the very beginning of the interacalation process) are due to spins in highly disordered domains. Line 'b' disappears as the intercalation process proceeds, supporting a recent Raman study on the same system which suggested that disordered domains are transformed into ordered domains as the intercalant density increases. We argue that both lines 'b' and 'a' (in the initial state of intercalation) are probably hyperfine split spectra due to interaction with the fluorine nuclei (I = 1 2), although we cannot rule out the possibility that line 'a' is associated with spins in ordered domains. At low temperatures lines 'a' and 'b' merge into a single line (line 'd') at g = 2.008 ± 0.003. This collapse is associated with changes in the signals' peak-to-peak heights. We suggest the formation of intercalant clusters and strain field as the origins of these effects. The intercalation of F₂ into the donor GIC C/K and C/Li gives very similar ESR properties. At low temperatures a new line appears at g = 2.035 ± 0.002 (line 'e') in all the three systems. This line is believed to be associated with a 'line dislocation' or 'domain wall'.