by P. Sheng.
Available online 12 August 2008.
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New C70 fullerides with compositions of MgxC70 at 1<x≤5 were prepared by solid state reaction. While most samples with 1<x<4 were multiphase, a single phase was obtained at x=5. Mg5C70 was found to be a Mg-saturated phase and its x-ray diffraction profile was successfully assigned to a simple orthorhombic structure with a=1.684, b=1.462, and . Mg5C70 was found to be non-metallic and exhibited an anomaly in magnetic susceptibility at approximately 80 K. No superconducting transition was found for MgxC70 (1<x≤5) down to a temperature of 2 K.
Keywords: A. Fullerenes; B. Chemical synthesis; E. Electron paramagnetic resonance
PACS classification codes: 61.48.+c; 71. 20. Tx
Fig. 1. Temperature-reaction time phase diagram for MgxC70 products. Symbols ○ and denote the formation of fullerides MgxC70 and amorphous-like products, respectively.
Fig. 2. XRD profiles for (a) C70 cage-collapsed MgxC70 and (b) pristine C70 at RT. The data was measured by using Mo Kα radiation (). Raman spectra for C70 cage-collapsed MgxC70 and pristine C70 are shown in (c) and (d), respectively. Arrows 1 and 2 in panel (c) indicate the positions of Raman spectral peaks characteristic of nanocrystalline graphite and amorphous carbon, respectively.
Fig. 3. XRD profiles for MgxC70 at x=0, 2, 3, 4 and 5, measured by using Mo Kα radiation () at RT.
Fig. 4. XRD profile of Mg5C70 at 298 K. The data was measured using SR (). All reflections are assigned to a simple orthorhombic structure.
Fig. 5. ESR spectra of Mg5C70 powder at 3.0, 140 and 300 K. The spectrum at 300 K could be reproduced using two respective Lorentzian functions.
Fig. 6. Temperature dependence of (a) the spin susceptibility χs estimated from the integrated ESR intensity, (b) the peak-to-peak line width ΔHpp, and (c) the g-value for the broad and narrow signals in Fig. 5, respectively.