XAFS STUDIES OF THE OXIDATION PROCESS IN RBXCSYC60 (X=3, Y=0 AND X=2, Y=1)

EXAFS measurements of the alkali-doped fullerene superconductors, RbxCsyC60 (x=3, y=0 and x=2, y=1 with T(c)=30 and 31 K, respectively), have been made at the Rb K-edge as a function of exposure time to O2 gas. The distances r(Rb-C)=3.35+/-0.02 and 3.31+/-0.02 angstrom were obtained for pristine RbxCsyC60 of x=3, y=0 and x=2, y=1, respectively, in good agreement with the reported value of 3.33 angstrom at the tetrahedral site determined by X-ray diffraction study. The analysis of the Rb-O EXAFS in Rb3C60 exposed to O2 for 40 h gives r(Rb-O)=2.89+/-0.05 angstrom and N=4+/-1, consistent with the crystallographic values of rubidium oxide (Rb2O: r(Rb-O)=2.91 angstrom and N=4 at room temperature). The result indicates that the Rb in RbxCsyC60 is converted into Rb2O through the oxidation.