Contribution of Embedded Bromine Molecules to the Dielectric Properties of Fluorinated Graphite Intercalation Compounds

Abstract

Here, we study the dielectric properties of fluorinated graphites C2Fx with different fluorine contents (x ≈ 1.05, 0.85, and 0.60) and embedded bromine molecules by impedance spectroscopy. An analysis of the results using the Maxwell-Garnett approximation made it possible to estimate the contributions of the fluorinated graphite matrix and bromine guests to the dielectric permittivity of the compound. The permittivity of the C2Fx matrix increases with decreasing fluorine content and does not depend on temperature. The change in the permittivity upon cooling/heating of the samples is provided by the polarization of bromine molecules Br2. The significant temperature-dependent dielectric response of C2F0.60 is associated with the formation of bromine and polybromide ions, such as Br2– and Br3–, in the interlayer space of the matrix. The decrease in the permittivity at low temperature is explained by the freezing of the ion mobility.