STRUCTURAL, MAGNETIC AND SUPERCONDUCTING PROPERTIES OF GRAPHITE NANOTUBES AND THEIR ENCAPSULATION COMPOUNDS

X-ray diffraction and magnetic susceptibility measurements have been made for graphite nanotubes and encapsulation compounds of TaC and CeC2. In the nanotubes the graphite layers expand 2.27% (c0 = 6.852 A) in the interlayer spacing, and only 0.09% in the in-plane direction. The observed (hk0) diffraction peaks show a pronounced asymmetric lineshape of the Warren type, which results from complete stacking disorder. The carbide inside the nanotube, which is a single crystal in most cases, has a lattice parameter very close to that of the carbide in the bulk, indicating no significant effect due to encapsulation. The superconducting T(c) of encapsulated TaC is very close to that of the bulk sample. An antiferromagnetic transition has been observed in the CeC2 encapsulation compound; the observed T(N) is consistent with that found in an earlier neutron study of a bulk sample.