1997 Fiscal Year Final Research Report Summary
Crystal and Electronic Structures of Fluorinated Fullerenes
| Project/Area Number |
08640643
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical chemistry
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| Research Institution | Shinshu University |
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Principal Investigator |
OKINO Fujio Shinshun University, Faculty of Textile Science and Technology, Associate Professor, 繊維学部, 助教授 (60214037)
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| Project Period (FY) |
1996 – 1997
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| Keywords | Fluorinated fullerenes / Fullerenes / X-ray structural analysis / Single crystal / Solid lithium battery / Electrochemistry / Electronic structure / Cyclic voltammetry |
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| Research Abstract |
Fluorination of fullerene C_<60> results in the formation of C_<60>F_x with C-F covalent bonds. The powder x-ray diffraction studies show that the spherical C_<60>F_x (x<approximately equal>46) molecules made of an inner carbon-atom sphere and an outer fluorine-atom sphere take the face-centered cubic structure. Single crystal growth of C_<60>F_x was successfully carried out and the radii of the carbon-atom sphere and the fluorine-atom sphere were determined. The lattice constant was determined to be 17.158(3) *. C_<60>F_<36> and C_<60>F_<48>, both with singular molecular species, have the body-centered cubic and body-centered tetragonal structures at room temperature. The latter shows a phase transition at ca.353 K into the face-centered cubic structure.
XPS,UPS and XANES spectroscopic studies on fluorinated fullerenes indicate that the fluorination of C_<60> reduces the extent of the pi-conjugate system, decreases the pi and pi^<**> band widths, and lowers the pi and pi^<**> band level by the induction effect of fluorine.
All solid state lithium batteries were constructed using C_<60>F_x and C_<70>F_x as cathodes with a polyphosphazene derivative as a lithium-ion conducting electrolyte. Charge-discharge measurements were made. The open-circuit voltages of the cells were ca.4.0 V and high cathode utilities of 90% were observed. The discharge occurs via the reduction of C-F bonds and the original fullerenes are expected to be the final discharge products.
The redox behaviors of C_<60>, C_<70>, C_<60>F_x and C_<70>F_x were investigated by cyclic voltammetry in CH_2Cl_2 solutions. The electron affinities of C_<60>F_<36>, C_<60>F_<46> and C_<70>F_<54> are estimated to be 3.48,4.23 and 4.42 eV,respectively. This confirms the lowering of the LUMO-pi^<**> level as a function of the number of added fluorine atoms.
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