Direct EELS observation of the oxidation states of Sm atoms in Sm@C-2n metallofullerenes (74 <= 2n <= 84)

The oxidation states of Sm atoms in various fullerene cages are directly in vestigated by electron energy-loss spectroscopy. The observed peak position s of the M-45 edges of the Sm atom in Sm@C-2n, [2n = 74, 78, 80, 82 (isomer s I, III), 84, (isomers I, II, III)] are apparently shifted to the lower bi nding energy region in comparison with those of a trivalent Sm3+ in Sm2O3. The results indicate that the Sm atoms take 12 valence states irrespective of the fullerene cages. This observation is discussed based on a simple the rmochemical cycle model. We also report that the Sm metallofullerenes have been converted to Sm carbide materials under a prolonged electron beam irra diation. (C) 2000 American Institute of Physics. [S0021-9606(00)Q1 645-7].