Syntheses of tin and lead fluoride graphite intercalation compounds and the phase transition of the tin fluoride compound

The reaction of tin tetrafluoride with graphite in liquid anhydrous hydrogen fluoride (AHF) in the presence of fluorine yields a stage-2 graphite intercalation compound (GIC) with an identity period Ic = 11.53 Å, whereas no intercalation reaction occurs without fluorine. With lead tetrafluoride, however, the reaction proceeds without fluorine yielding a stage-2 compound. X-ray diffraction and differential scanning calorimetry measurements on the SnF4-based GICs confirmed a two-dimensional phase transition over a wide temperature range from 120 to 170 K. The optical reflectivity in the UV-Vis region on the SnF4-based GICs has also been studied as a function of stage number. The experimental results were analyzed using the Blinowski-Rigaux model. It was found that the reflectivity minimum shifts towards lower energy with the increase of stage number. This behavior is attributed to the increase of carrier density. The charge transfer per carbon atom in CxSnF6 does not differ greatly from those in C6F and C16AsF5. The derived electrical conductivity of CxSnF6 is not as high as that of C16AsF5 owing to the shorter mean free path of the carriers in the former as a consequence of lattice defects generated in the course of the intercalation in the AHF solutions.