S. Fujiki

Structure and electronic properties of Dy@C82 studied by UV–VIS absorption, X-ray powder diffraction and XAFS

Abstract Two isomers of Dy@C 82 were separated by high performance liquid chromatography (HPLC), and their UV–VIS absorption spectra were measured to characterize these isomers. The crystalline powder of Dy@C 82 was obtained by removing the solvent (toluene) at 250°C under vacuum. The X-ray diffraction pattern can be indexed with fcc crystal lattice, as that in La@C 82 . The lattice constant a at 298 K, 15.86(1) A, is close to that of La@C 82 , 15.78 A. The distances between Dy and the first and second nearest C atoms are determined to be 2.52(2) and 2.86(2) A, respectively, on the basis of Dy L III -edge EXAFS. The XANES shows that the valence of the Dy atom in Dy@C 82 is +3.

XAFS study on metal endohedral fullerenes

Structure of metal endohedral fullerenes is studied by XAFS and XANES. The Sc-Sc distance of 2.23(1) A determined from Sc K-edge XAFS supports the formation of a triangular Sc3 cluster in Sc3@C82 as is found by MEM analysis for the X-ray diffraction. Gd L(III)-edge XAFS of Gd@C82 shows that the first and the second neigboring Gd-C distances are 2.51(2) and 2.85(4) A, respectively. The La-La distance of La2@C80 has been determined to be 3.90(1) A at 40 K. This value does not change when increasing temperature [3.90(2) A at 240 K]. The position and the valenece of the Eu atom in Eu@C60 are also discussed based on Eu L(III)-edge XAFS and XANES.

XAFS study on a pressure-induced superconductor Cs3C60 under high pressure.

Cs K-edge XAFS of Cs3C60 which is a pressure-induced superconductor were measured at 21 and 34 kbar by using a diamond anvil cell (DAC) in order to obtain the structural information under high pressure, and to clarify the origin of the pressure-induced superconductivity. The distances and the mean square displacements between the Cs and C atoms are consistent with those determined by X-ray powder diffraction. Consequently, the high-pressure XAFS can give the reliable structural-information on a fullerene superconductor under high pressure. We also show the procedure of the analysis of high-pressure XAFS with DAC in detail.

Raman study of Cs3C60 under ambient pressure

Abstract Temperature dependence of Raman scattering in a pressure-induced superconductor Cs3C60 was studied under ambient pressure between 2 and 290 K. The contributions of the intramolecular vibration modes to electron–phonon coupling were evaluated by comparing the linewidths of the modes in Cs3C60 with those in pristine C60. The total electron–phonon coupling constant λ was ≈0.18, approximately one-third of the values for Rb3C60 and K3C60. Temperature-dependent Raman scattering in the superconductor Rb3C60 and a non-superconductor Rb6C60 was also measured for comparison.

Structure and physical properties of Cs3C60 under ambient and high pressures

Structure and physical properties of a pressure induced superconductor Cs3C60 were studied by X-ray powder diffraction and ESR methods. All X-ray diffraction patterns below 300 K under ambient pressure (1 bar) showed that Cs3C60 took a body-centered orthorhombic (bco) structure as main phase and an A15 structure as minor phase. The ESR at 1 bar showed that Cs3C60 was metallic from 2 to 290 K. The pressure dependence of X-ray powder diffraction showed a disappearance of A15 phase above 20 kbar. The compressibility for the bco phase of Cs3C60, 3.1×10−3 kbar−1, was similar to those of Rb3C60 and K3C60

Study on the physical properties of Na4C60

Temperature dependence of resistivity, ρ, of a two-dimensional polymer phase of Na4C60 has been studied from 190 to 300 K. The ρ was 6.9×103 Ω cm at 300 K, which is higher by six orders than those of metallic fullerides. The temperature dependence of ρ shows a semiconducting behavior in this temperature region. This result is different from the previous result derived from ESR which suggests a metallic property above 100 K. The gap energy, Eg, was estimated to be 0.8 eV. This value is close to those of other A4C60 (A:K, Rb and Cs).

Study on the origin of pressure-induced superconductivity of Cs3C60

Physical properties of bco phase of Cs3+αC60 (α=0.0−1.0) and A15 phase of Cs3C60 are studied by X-ray diffraction, ESR, AC susceptibility, resistivity and Raman. The ESR of Cs300(6)C60 showed a broad peak of ∼380 G due to conduction electron, while no broad peak was observed in the ESR of bco Cs3+αC60 (α≠0.0) and A15 phase. This shows that only bco phase of Cs3C60 is metallic. The AC susceptibility of bco phase of Cs3.2(3)C60 and Cs3.5(1)C60 showed no superconducting transition above 1.3 K even under high pressure, and the resistivity was 0.52 Ω cm for both samples.

X-ray diffraction of Na4C60 at low temperature under high pressure

X-ray diffractions of two-dimensional Na4C60 are studied at various temperatures above 11 K in a pressure region up to 67 kbar. All X-ray diffraction patterns measured in this study can be analyzed by using a body-centered monoclinic (bcm) structure of space group I2/m. New Bragg reflections which cannot be assigned to I2/m are not observed in all X-ray diffraction patterns. The β at 11 K and 67 kbar is the smallest (93.66(8)°) among those of Na4C60 lattice of bcm. In this crystal, the center-to-center distance, 9.57(2) A, between the C60 molecules associated with van der Waals contacts approaches to that, 9.20(2) A, between the C60 molecules in a polymer chain, suggesting the realization of three-dimensional polymeric structure in Na4C60 at a higher pressure than 67 kbar.