XAFS studies of the oxidation process in Rb_xCs_yC₆₀ (x=3, y=0 and x=2, y=1)

EXAFS measurements of the alkali-doped fullerence superconductors, Rb_xCs_yC₆₀ (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 Å were obtained for pristine Rb_xCs_yC₆₀ of x=3, y=0 and x=2, y=1, respectively, in good agreement with the reported value of 3.33 Å 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 Å and N=4±1, consistent with the crystallographic values of rubidium oxide (Rb₂O: r_Rb-O=2.91 Å and N=4 at room temperature). The result indicates that the Rb in Rb_xCs_yC₆₀ is converted into Rb₂O through the oxidation.