Characterizing high-pressure compressed C 60 whiskers and C 60 powder
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Yusuke Kuwasaki Department of Materials Engineering, School of Engineering, The University of Tokyo, 7-3-1, Hogno, Bunkyo-ku, Tokyo, 113-8656, Japan
Tadatomo Suga Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo, 153-8904, Japan (Received 26 August 2002; 18 October 2002)
Structural, mechanical, and electrical properties were examined for C60 whiskers, high-pressure sintered C60 whiskers, and C60 powder. A high density of dislocations was observed in the C60 whiskers, and the C60 whiskers with diameters of a few hundred nanometers were found to be flexible. Although both the specimens sintered under the same condition showed similar surface x-ray diffraction profiles with a strong accumulation of [110]tr orientation, the sintered C60 whiskers showed a higher micro-Vickers hardness and an electrical resistivity four orders of magnitude lower than that of the sintered C60 powder.
I. INTRODUCTION
Single-crystalline whiskers of C60 were found in a sol containing alkoxide precursors of lead zirconate titanate (PZT), and the C60 whiskers with submicrometer diameters were specially named “C60 nanowhiskers.”1 The C60 whiskers have growth axes parallel to the closepacked direction of C60 molecules and can be repeatedly produced by the liquid–liquid interfacial precipitation (LLIP) method at room temperature, where the C60 whiskers nucleate at the interface between a toluene solution of C60 and isopropyl alcohol.2 In 1994, Pekker et al. fabricated K-doped C60 whiskers by partial oxidation of K1C60 single crystals.3 Their K-doped C60 whiskers had a degree of polymerization greater than 100,000 with a typical thickness of 2–5 m, while our liquid-phasesynthesized C60 whiskers reach a degree of polymerization greater than 500,000 along the whisker growth axis, and their thickness can be less than about 150 nm. The pristine C60 crystals have a face-centered-cubic (fcc) structure where the C60 molecules are bonded via weak van der Waals force, while the liquid-phase-synthesized C60 whiskers consist of the C60 molecules linearly polymerized along the whisker growth axis.2 This LLIP method was tested for C70, and singlecrystalline nanowhiskers of C70 were successfully fabricated as well.4 Further, iodine-doped C60 whiskers were synthesized recently by the LLIP method, using an isopropyl alcohol solution of iodine and a toluene solution of C60.5 The iodine-doped C60 whiskers showed 166
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J. Mater. Res., Vol. 18, No. 1, Jan 2003 Downloaded: 12 Mar 2015
nonlinear current–voltage curves. However, various physical and chemical properties of our liquid-phasesynthesized C60 whiskers have not been sufficiently investigated. On the other hand, it has been shown that C60 molecules are polymerized under a high pressure and a high temperature.6 It is of great interest to investigate differences in the properties between the high-pressuresintered C60 whiskers and the high-pressure-sintered C60 powder, since the high-pressure-sintered C60 whiskers are ex
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