Raman scattering as a probe of structural phase transitions in the intercalated graphite-bromine system

Results of the temperature-dependent Raman spectra of graphite-bromine intercalation compounds are reported in the temperature range $290<T<\mathrm{}380\mathrm{}$ K. Of particular importance is the first observation of phase transitions in intercalated graphite using the Raman scattering technique, including (1) a commensurate-incommensurate phase transition and (2) a melting transition in the intercalate bromine layer. For a stage-3 compound, the commensurate-incommensurate phase transition occurs at $T_0=335\mathrm{}\pm 10$ K, while the melting transition occurs continuously from 345 to 380 K. The temperature dependences of the Raman line shape, linewidth, frequency, and the intensity of the intercalate bromine molecular stretch mode have been utilized to investigate the phase transitions. The amount of charge transfer per intercalate bromine molecule has been estimated to be 0.34 by using the frequency shift of the intercalate bromine molecular stretch mode.