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Fullerenes, Nanotubes andCarbon NanostructuresPublication details, including instructions forauthors and subscription information:http://www.tandfonline.com/loi/lfnn20

C60 Intercalated Graphite: ANew Form of CarbonVinay Gupta a , Peter Scharff a , Loredana CartaAbelmann a & Lothar Spiess ba Institute of Physics , Ilmenau Technical University ,Ilmenau, Germanyb Institute of Materials Science , Ilmenau TechnicalUniversity , Ilmenau, GermanyPublished online: 06 Feb 2007.

To cite this article: Vinay Gupta , Peter Scharff , Loredana Carta Abelmann & LotharSpiess (2005) C60 Intercalated Graphite: A New Form of Carbon, Fullerenes, Nanotubesand Carbon Nanostructures, 13:S1, 427-430, DOI: 10.1081/FST-200039421

To link to this article: http://dx.doi.org/10.1081/FST-200039421

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C60 Intercalated Graphite: A NewForm of Carbon

Vinay Gupta, Peter Scharff, and Loredana Carta Abelmann

Institute of Physics, Ilmenau Technical University, Ilmenau, Germany

Lothar Spiess

Institute of Materials Science, Ilmenau Technical University,

Ilmenau, Germany

Abstract: A carbon solid containing two carbon allotropes, C60 and graphite has been

synthesized. In this solid, the two dimensional layers of C60, stacked in between every

graphite layers, show long range ordering with average separation of 1.27 nm between

C60 layers. Predominantly stage-1 along with stage-4 is obtained. An up-shift in the

graphite E2g2 Raman mode and a downshift in the C60 Raman Ag2 mode occurred

due to a charge transfer and indicated highly conducting state of C60. This C60-

graphite intercalation compound can act as a host for co-intercalation of alkali-

metals and may lead to a new superconductors.

Keywords: Graphite, C60, fullerene, intercalation

INTRODUCTION

Both graphite and fullerenes have shown the ability to intercalate a wide

variety of atoms and molecules. The most interesting of them are alkali

metals, which induce superconducting behavior into both graphite and fuller-

enes, upon intercalation. In the case of alkali fullerides, superconducting tran-

sition temperature as high as 33 K (1) has been achieved. To break this barrier,

Address correspondence to Vinay Gupta, Environment and New Energy, KASTEC,

Kasuga-shi, Fukoka 816-8560, Japan. E-mail: drvinaygupta@netscape.net

Fullerenes, Nanotubes, and Carbon Nanostructures, 13: 427–430, 2005

Copyright # Taylor & Francis, Inc.

ISSN 1536-383X print/1536-4046 online

DOI: 10.1081/FST-200039421

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new ways of synthesizing C60 intercalation compounds are of great import-

ance. A preliminary theoretical study of Saito et al. (2) indicated that C60-

graphite intercalation compound are energetically stable and can become

superconducting upon intercalation with alkali metals. This was further

confirmed when Fuhrer et al. (3) co-intercalated C60 into K-graphite system

and obtained a resistive transition at 19.5 K, but only in a small fraction of

the samples in irreproducible manner, which may be due to poor ordering

of C60 into graphite. Here we describe, a recently pioneered pure C60-

graphite intercalation compound (4), an all-carbon solid, by directly

combining C60 and graphite.

EXPERIMENTAL

The type of graphite and method of intercalation are described elsewhere

(4, 5). In brief, C60-graphite intercalation compounds were synthesized by

treating C60 (99.95% pure) and graphite at 6008C in a vacuum-sealed quartz

tube for 2 weeks. Transmission electron microscopy measurements were

done on a Tecnia 20S-TWIN TEM operating at electron accelerating

voltage of 200 kV and Raman spectroscopy measurements at 488 nm (blue

laser).

RESULTS AND DISCUSSION

High-resolution transmission electron microscopy (HRTEM) images of the

Stage-4 and Stage-1, C60-graphite are shown in Fig. 1a and 1d, respectively

(the number of graphene layers between two intercalate layers is referred to

as the stage number). A HRTEM image of Stage-1 C60-graphite is shown in

Fig. 1b. The average distance between two adjacent parallel layers was

1.27 nm. This material showed hexagonal symmetry. The radius of C60 can

be taken as 0.355 nm. The van der Waals gap is 0.29 nm in the case of

C60-graphite. By adding these values, the calculated C60 center-to-center

distance for Stage-4 and Stage-1 are shown in Fig. 1b and 1e, respectively,

in good agreement with the experimentally obtained value.

Raman spectroscopy is a powerful tool for studying the phonon character-

istics of graphite intercalation compounds (GICs) of both donor and acceptor

type. In particular, the stage dependence of Raman active E2g2 mode reveals

that charge density in the graphitic layers in contact with an intercalated

species is different from that of the graphitic layers that are not in contact.

Hence, graphite E2g2 mode split for stages � 2 and the original graphite

E2g2 mode disappears completely for pure Stage-1 GICs. In the case of

acceptor guest species, Raman active E2g2 mode of graphite up-shifts from

its 1582 cm21 position and exceed the 1600 cm21 value but in the case of

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C60 intercalated graphite, a low charge transfer and hence a low up-shift was

predicted by Saito and Oshiyama (2). The Raman spectra of the Stage-4 and

Stage-1 C60-graphite are shown in Fig. 1c and 1f. The original graphite E2g2

mode up-shifted from its usual 1582 cm21 position, for Stage-4 and Stage-

1, to 1586.6 cm21 and 1589.1 cm21 values, respectively due to electron

Figure 1. Transmission electron microscopy images of Stage-4 C60-graphite (a),

Stage-1 C60-graphite (d). Schematic diagrams with calculations, of Stage-4 C60-graph-

ite (b), Stage-1 C60-graphite (e). Raman spectrum of Stage-4 C60-graphite (c), Stage-1

C60-graphite (f).

C60 Intercalated Graphite 429

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transfer from graphite to C60. C60 can behave as an electron acceptor similar to

alkali-metal intercalated fullerenes (6). Pentagonal pinch mode (Ag2) of

pristine C60 at 1469 cm21 was down-shifted (6) to 1446.1 cm21 (6) after inter-

calation. An electron transfer from graphite to C60 can partially fill the t1u level

(6) of C60 and contribute its conductivity by making it highly conducting, and

it may be superconducting. The peak at 1370 cm21 may be due to increased

disorder. Finally, novel C60-graphite systems can be a potential host for

new co-intercalation of alkali metals and can lead to better superconductors

with high Tc.

ACKNOWLEDGMENTS

This work was financially supported by the Humboldt foundation.

H. Romanus, R. Muller, and K. Risch are thanked for technical assistance.

REFERENCES

1. Tanigaki, K., Ebbesen, T.W., Saito, S., Mizuki, J., Tsai, J.S., Kubo, Y., andKuroshima, S. (1991) Superconductivity at 33 K in CsxRbyC60. Nature, 352:222–224.

2. Saito, S. and Oshiyama, A. (1994) Design of C60-graphite intercalation compounds.Phys. Rev. B, 49: 17413–17419.

3. Fuhrer, M.S., Hou, J.G., Xiang, X.D., and Zettl, A. (1994) C60 intercalated graphite:Prediction and experiments. Solid State Commun., 90: 357–360.

4. Gupta, V., Scharff, P., Risch, K., Romanus, H., and Muller, R. (2004) Synthesis ofC60 intercalated graphite. Solid State Commun., 131: 153–155.

5. Chen, G., Wu, D., Weng, W., and Wu, C. (2003) Exfoliation of graphite and itsnanocomposites. Carbon, 41: 619–621.

6. Duclos, S.J., Haddon, R.C., Glarum, S., Hebard, A.F., and Lyons, K.B. (1991)Raman studies of alkali-metal doped AxC60 films (A ¼ Na, K, Rb & Cs; X ¼ 0,3, 6). Science, 254: 1625–1627.

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