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 hy drogen fluoride (AHF) in the presence of fluorine yields a stage-2 gra phite intercalation compound (GIC) with an identity period I-c = 11.53 Angstrom, whereas no intercalation reaction occurs without fluorine. With lead tetrafluoride, however, the reaction proceeds without fluori ne yielding a stage-2 compound. X-ray diffraction and differential sca nning 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 W-Vis region on the SnF4-based GICs has also been studied as a function of stage number. The experim ental results were analyzed using the Blinowski-Rigaux model. It was f ound that the reflectivity minimum shifts towards lower energy with th e increase of stage number. This behavior is attributed to the increas e of carrier density. The charge transfer per carbon atom in CxSnF6 do es not differ greatly from those in C6F and C16AsF5. The derived elect rical conductivity of CxSnF6 is not as high as that of C16AsF5 owing t o the shorter mean free path of the carriers in the former as a conseq uence of lattice defects generated in the course of the intercalation in the AHF solutions.