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 xtructural 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.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry