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)


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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