Design and Control of Graphite Intercalation Reactions in Liquid Hf.

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1. Involatile Fluoride-GIC.We have found a new synthetic pathway to involatile fluoridebased in liquid AHF which is saturated with fluorine gas and the species to be intercalated. The intercalation reaction proceeds through the substitution of bifluoride by fluorometallate as follows ;C_x + 1/2F_x + HF -> C_xHF_2 + MF^-_2An attractive feature of this method is that the stage can be controlled by changing the concentration of fluorometallate in ahf. This preparative method has been giving a series of new C_xMF_y based on involatile fluorides, SnF_4, PbF_4, CrF_4, SbF_4, RhF_3, and LiBF_4.2. The study of X-ray precession patterns of a crystal of composition C_<30>SnF_5 has shown that the lattice of the intercalate is incommensurate with the a-parameter of graphite. The local environment of tin in both SnF_4 and C_<30>SnF_5 has been determined from EXAFS. The first coordination shell is formed of axially flattened octahedra of fluoride ion.3. A ^<11OMEGA>Sn Mo^^"ssbauer resonance investigation has been performed over the temperature range 4.2<T<293K on C_<30>SnF_5. At room temperature, a single is observed. A sizable broadening occurs with decreasing temperature, and between 160K and 140K a doublet appears owi ng to a strong quadrupole splitting. These results suggest a two-dimensional phase transition of the guest species.4. Charge transfer has been evaluated in stage-2 C_xCrF_y and C_xRhF_y GICs by optical measurements. Charge transfer coefficients f=0.50 and f=0.59 per intercalated species have been determined from reflectivity date using the Blinowski-Rigaux model. The fermi energies have also been evaluated from the optical measurements. E_F values are 0.94 and 0.89eV for C_xCrF_y and C_xRhF_y, respectively.