Raman scattering study of acceptor-acceptor-type graphite bi-intercalation compounds

Abstract

Stages 4 and 5 ${\mathrm{FeCl}}_{3}$-graphite intercalation compounds (GIC's) were prepared by a two-bulb method, and were used as host materials for the synthesis of graphite bi-intercalation compounds (GBC's), where the bi-intercalated species were ICl, IBr, and ${\mathrm{SbCl}}_{5}.$ Various types of GBC's were obtained by changing the reaction temperatures, and the layer sequences were clarified by x-ray diffraction. Lattice dynamics of the resultant GBC's was investigated by Raman spectroscopy. Since the layer sequence of GBC's from a stage 4 ${\mathrm{FeCl}}_{3}\ensuremath{-}\mathrm{G}\mathrm{I}\mathrm{C}$ with one bi-intercalated layer is ${\mathrm{G}(\mathrm{F}\mathrm{e}\mathrm{C}\mathrm{l}}_{3}{)\mathrm{G}}_{1}{\mathrm{G}}_{2}{(\mathrm{I})\mathrm{G}}_{3}{\mathrm{G}}_{4}{(\mathrm{F}\mathrm{e}\mathrm{C}\mathrm{l}}_{3})\mathrm{G},$ where ${\mathrm{G}}_{n},$ $({\mathrm{FeCl}}_{3}),$ and (I) denote the $n\mathrm{th}$ graphite, ${\mathrm{FeCl}}_{3},$ and bi-intercalated layers, respectively, and all graphene layers are adjacent to an intercalate layer. The GBC's give only one Raman-active ${E}_{2g}^{(2)b}$ mode frequency in the Raman spectra although the intercalates are different. GBC's from stage 5 ${\mathrm{FeCl}}_{3}\ensuremath{-}\mathrm{G}\mathrm{I}\mathrm{C}$ with one bi-intercalated layer give the stacking sequence of ${\mathrm{G}(\mathrm{F}\mathrm{e}\mathrm{C}\mathrm{l}}_{3}{)\mathrm{G}}_{1}{\mathrm{G}}_{2}{(\mathrm{I})\mathrm{G}}_{3}{\mathrm{G}}_{4}{\mathrm{G}}_{5}{(\mathrm{F}\mathrm{e}\mathrm{C}\mathrm{l}}_{3})\mathrm{G}.$ Since two types of graphene layers, interior $({\mathrm{G}}_{4})$ and bounding $({\mathrm{G}}_{1,2,3,5})$ layers exist, two peaks identified as Raman-active ${E}_{2g}^{(2)i}$ and ${E}_{2g}^{(2)b}$ mode frequencies appear in Raman spectra. Both frequencies were affected by the bi-intercalated species. From the ${E}_{2g}^{(2)i}$ frequencies, the degree of electron affinities of the bi-intercalated layers was evaluated to be in the order of ${\mathrm{IBr}l\mathrm{ICl}l\mathrm{SbCl}}_{5}.$ For the GBC's with two bi-intercalated layers, their layer sequences were determined to be ${\mathrm{G}(\mathrm{F}\mathrm{e}\mathrm{C}\mathrm{l}}_{3}{)\mathrm{G}\mathrm{G}(\mathrm{I})\mathrm{G}(\mathrm{I})\mathrm{G}\mathrm{G}(\mathrm{F}\mathrm{e}\mathrm{C}\mathrm{l}}_{3})\mathrm{G}$ or ${\mathrm{G}(\mathrm{F}\mathrm{e}\mathrm{C}\mathrm{l}}_{3}{)\mathrm{G}\mathrm{G}(\mathrm{I})\mathrm{GG}(\mathrm{I})\mathrm{G}(\mathrm{F}\mathrm{e}\mathrm{C}\mathrm{l}}_{3})\mathrm{G}.$ In this case, only bounding layers of graphite exist. However, two peaks were observed in the Raman spectra. The difference of the Raman-active ${E}_{2g}^{(2)b}$ mode frequencies was due to the intercalate coupling effect.