Position of K Atoms in Doped Single Walled Carbon Nanotube Crystals
Gao, G., Cagin, T. and Goddard, W. A.
Phys. Rev. Lett. 80, 5556 (1998)
ABSTRACT
Recent experiments by Lee et al. [Nature 363, 255 (1997)],
show that doping carbon single
wall nanotube (SWNT) ropes with K, Rb,
or Br2 leads to metallic conductivity; but, the structure and
properties are not known. We
used theory [quantum mechanics (QM) and molecular dynamics (MD)] to
predict structures and properties which should help motivate and interpret
experiments on SWNT/K. Assuming that the K cannot penetrate the
tubes, we find the optimum stoichiometry to be KC16.
We predict the optimum structure
and the associated powder
diffraction X-ray pattern expected for KnC80 from n = 0 to
10 (optimum is n = 5) for both trigonal (closest packed) and square
packing of the tubes. The Young's modulus per tube along the tube
axis from
640 to 525 GPa for n = 0 to 5. Assuming that K can penetrate inside the tubes
(perhaps at defects or through open ends) leads to an optimum
stoichiometry of K1C10
K5exoK3endoC80 with 3
within the tube).
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