A novel stable solid formed by C 60 + oxygen at high P(O 2 )
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We report the formation of a novel solid form of carbon + oxygen. Exposure of C6o to high oxygen pressure [P(O2) = 100 MPa] for several days at slightly above ambient temperature results in absorption of significant amounts of oxygen (up to ~ 4 8 % by weight after 3 days). X-ray diffraction measurements showed that the C60 pellets had become amorphous. Although part of the added weight is slowly lost in flowing oxygen at ambient pressure and temperature, most remains up to at least 100 °C. Heating in flowing He at 200 °C brought the weight back to near the original value. The reaction appears to be specific to C6o since the amorphous outgassed material had lost the capacity to absorb oxygen at high P(O 2 ), and the oxygen absorption effect was absent in powdered graphite and in commercial amorphous carbon. The Raman spectrum differs from those of C6o, soot, amorphous carbon, graphite, and diamond.
I. INTRODUCTION Several interesting results on the interaction of oxygen with C6o have been reported in the literature. It was found that C60 could produce singlet oxygen in high yield.1 Kroll et al.2 reported that C60 was oxidized by solid O 2 on exposure to photons. Vijayakrishnan et al? found evidence of reactive interaction at the surface of the C60 film in the XPS studies. Reversible insertion of O 2 into the fee lattice of C6o was reported for the first time by Schirber et al.4 This was achieved by hydrostatic pressure of O 2 . The NMR investigation suggested that six O 2 molecules were present in the six octahedral holes around a C6o molecule. However, at a pressure of 1000 bar at room temperature only 15% of the available octahedral sites were filled; the corresponding weight increase is 0.67%. We have studied the C 6 o - 0 2 system in high oxygen pressure. We find a much larger uptake of oxygen. At high oxygen uptake the C 60 crystalline structure is destroyed and one gets an amorphous material. However, instead of decomposing to volatile CO and/or CO 2 , the oxygen and carbon remain bound in a solid at ambient temperature. Although our samples were treated in about the same oxygen pressure as reported by Schirber et al.,4 the weight gain in our samples was up to 48% orders of magnitude larger. The reason for this difference is not known.
a commercially available high pressure oxygen furnace.5 The sample holder was situated outside the heating zone in the high-pressure furnace vessel and separated by a barrier which ensured that the sample temperature was close to room temperature (
