Structural and Electronic Characterizations of Two Isomers of Ce@C₈₂

Abstract

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.

Magnetic Properties and Crystal Structure of Solvent‐Free Sc@C82 Metallofullerene Microcrystals

“…[39][40][41][42] Temperature dependence of the physical properties of such metallofullerene solids or single crystals has been also characterized by ESR, SQUID magnetic measurements [43][44][45][46][47][48][49][50] and X-ray diffraction measurements. [51,52] Antiferromagnetic-like interactions have been observed for powder crystals of La@C 82 , [44] Gd@C 82 [43,44] and heavy rare-earth monometallofullerenes [48] by the SQUID magnetic measurements.…”

Metallic phase in the metal-intercalated higher fullereneRb8.8(7)C84

“…Consequently, we carried out the Rietveld refinement with the space group Pa3 in the same manner as M@C 82 and C 82 . [4][5][6][7][8]14 The major phase, Rb x C 84 ͑D 2d ͑23͒͒, was used in the refinement. The principal C 2 axis of D 2d -C 84 extends along ͓111͔ ͓Fig.…”

“…Recently, it was found that M@C 82 is not metallic but semiconductorlike, regardless of the fact that odd numbers of electrons are transferred to the C 82 cage from the encapsulated metal atom. [5][6][7][8][9][10][11] However, the metallic behavior found in Rb 8.8͑7͒ C 84 can be explained by the simple band picture, as in the case of alkaline metal doped C 60 . 1 This indicates the possibility of materials design with higher fullerenes conducted by theoretical calculation.…”

“…The photoemission ͑UPS͒, 9 resistivity , 5,7,8 optical spectroscopy 10 and scanning tunneling spectroscopy ͑STS͒ ͑Ref. 11͒ showed a semiconductorlike behavior with small energy gap, E g , for M@C 82 where the valence of M is +3.…”

“…1 Recently, crystalline solid samples of metallofullerenes and higher fullerenes were obtained, and their structures have been studied by x-ray powder diffractions. [4][5][6][7][8] The crystals of M@C 82 ͑M = lanthanide atoms͒ showed a cubic structure of space group Pa3 ͓a = 15.78͑1͒ Å for Dy@C 82 , 15.78͑1͒ Å for the C 2v isomer of Ce@C 82 , and 15.74͑4͒ Å for the C s isomer of Ce@C 82 ͔.…”