X-ray diffraction patterns for a solid sample of Ce@C 82 that contains a mixture of two isomers, I and II, can be indexed in a face-centered cubic lattice with a lattice constant of 15.88͑5͒ Å, while x-ray diffraction patterns for Ce@C 82 isomer I alone indicate a simple cubic lattice with a lattice constant of 15.78͑1͒ Å. Rietveld refinement for the x-ray diffraction pattern of the latter, Ce@C 82 isomer I, has been carried out with a space group of Pa3 . Thin films of Ce@C 82 were first prepared by thermal deposition under ϳ10 Ϫ7 Torr. The Raman spectra for these thin films show a peak ascribable to a Ce-C 82 cage-stretching mode at ϳ160 cm Ϫ1 , implying that the valence of Ce in this structure is ϩ3. This valence of ϩ3 is supported by Ce L III -edge XANES for a thin film of Ce@C 82 . Furthermore, the local structure around the Ce ion could be determined by Ce L III -edge EXAFS for a thin-film. Transport properties of a thin film of Ce@C 82 have been studied by a four-probe method, and these demonstrate a semiconducting behavior with a small gap of 0.4 eV.

X-ray diffractions and electronic transports for the Ce@C 82 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 Pa3 h. 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@C 82 isomer I in contrast with La@C 82 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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