Fullerenes and fulleroids: Stability, structure and properties

Krzysztof Wladystaw Kniaz, University of Pennsylvania

Abstract

In this thesis work several aspects of intercalation chemistry of C$\sb{60}$ were investigated. We studied n-doping of C$\sb{60}$ with alkali metals with emphasis on the structure of $\rm Na\sb2RbC\sb{60},$ p-doping using halogenes and finally doping using the C$\sb{70}$ molecule. Rietveld refinements of x-ray powder profiles show that the C$\sb{60}$ molecules in $\rm Na\sb2RbC\sb{60}$ are orientationally ordered in a manner essentially the same as in pure $\rm C\sb{60}$. Fits to data at both 300 K and 27 K are best in space group Pa3 (simple cubic). This result and published thermodynamic data suggest, that anomalously low T$\sb{\rm c}$ for $\rm Na\sb2RbC\sb{60}$ is caused by a different ground state, than in other fullerene superconductors. Solid $\rm C\sb{60}$ reacts with fluorine at 300K, yielding yellow-to-white solids, with average compositions in the range $\rm C\sb{60}F\sb{35-44}.$ Mass spectrometry reveals broad distributions of F/C$\sb{60}$. Infrared and other data indicate that fluorines attach externally to the fullerene skeleton. Most of the material sublimes in vacuum at 300$\sp\circ$C. X-ray analysis of the highly crystalline sublimate yields an average C-F bond length 1.49 A. Contact angle measurements of films prepared by spin-coating from solutions suggest potentially interesting lubricating properties, however low stability of fluorinated fullerenes precludes their practical use. Reaction between molecular iodine and C$\sb{60}$ yields and intercalation product $\rm C\sb{60}I\sb{3.67}$ in which layers of C$\sb{60}$ are separated by sheets of iodine. The compound is highly crystalline and creates a trigonal lattice with no charge transfer between C$\sb{60}$ and I$\sb2$ molecules. Interactions between IBr and C$\sb{60}$ were also investigated. X-ray diffraction and FTIR results show that unlike I$\sb2$, IBr creates an exohedral solid with iodines and bromines bonding to the carbons of the cage. The compound (C$\rm\sb{60}(IBr)\sb2)$ crystallizes in a monoclinic unit cell. The results of studies on $\rm C\sb{60}(x)$-$\rm C\sb{70}(1-x)$ fullerene alloys are presented. Dilute alloys prepared from toluene exhibit a large miscibility gap for 0.04$<$ x $<$0.95. In contrast, alloys prepared by sublimation are miscible in all proportions, in the high-temperature fcc phase. The experimental solubilities are compared with the calculated binary phase diagram, in which intermolecular interactions are treated by the Girifalco potential. This potential was also used to calculate solid state properties for the fcc phase of C$\sb{70}$.

Subject Area

Materials science

Recommended Citation

Kniaz, Krzysztof Wladystaw, "Fullerenes and fulleroids: Stability, structure and properties" (1996). Dissertations available from ProQuest. AAI9627946.
https://repository.upenn.edu/dissertations/AAI9627946

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