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Structural and Electronic Characterizations of Two Isomers of Ce@C82

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posted on 10.06.2004 by Yoshie Rikiishi, Yoshihiro Kubozono, Tomoko Hosokawa, Kana Shibata, Yusuke Haruyama, Yasuhiro Takabayashi, Akihiko Fujiwara, Shinichiro Kobayashi, Satoshi Mori, Yoshihiro Iwasa
X-ray diffractions and electronic transports for the Ce@C82 isomers I and II, which refer to major and minor isomers, respectively, are studied in a wide temperature region to clarify the structural and electronic properties characteristic of individual isomers. The X-ray diffraction patterns observed at 295 K can be indexed based on simple cubic (sc) structures with lattice constants, a's, of 15.78(1) Å for isomer I and 15.74(4) Å for isomer II. Rietveld analyses are achieved for these X-ray diffraction patterns with a space group of Pa3̄. Temperature dependence of a for isomer I shows a drastic change around 170 K, which implies existence of a structural phase transition. The structural phase transition above 300 K cannot be detected for Ce@C82 isomer I in contrast with La@C82 isomer I in which the phase transition at 400 K was detected by differential scanning calorimetry and dielectric constant measurements. The temperature dependence of a for isomer II indicates no structural phase transition from 100 to 300 K. The pressure dependence of a for isomer I exhibits a monotonic decrease with an increase in pressure. This result implies no pressure-induced structural phase transition for isomer I. The temperature dependence of resistivities for thin films of these isomers is studied by a four-probe method, and it shows narrow-gap semiconductor-like behaviors. The energy gaps of isomers I and II are 0.33 and 0.55 eV, respectively. The difference in the structural and electronic properties among the isomers of metallofullerenes will attract much interest in chemistry and materials science.

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