Structural properties of carbon peapods, ${\mathrm{C}}_{60}$, trapped into single-walled carbon nanotubes (SWNT), have been studied under high-pressure/high-temperature conditions (HPHT) by in situ x-ray diffraction. The ${\mathrm{C}}_{60}$ chain structure together with the influence of the filling on the SWNT change under HPHT treatment is investigated. Synthesis of a one-dimensional polymer chain of ${\mathrm{C}}_{60}$ inside the single-walled carbon nanotubes is evidenced. At $4\mathrm{GPa}$, increasing the temperature up to $1023°\mathrm{C}$ leads to a progressive ${\mathrm{C}}_{60}$ polymerization that is associated to a shortening of ${\mathrm{C}}_{60}\text{−}{\mathrm{C}}_{60}$ distance down to $8.7\mathrm{\AA }$. Back to ambient conditions, the ${\mathrm{C}}_{60}$ chain remains polymerized, emphasizing the high stability of this material. In addition, our data strongly suggest a symmetry change of the two-dimensional bunde lattice under pressure.

• Received 11 September 2006

DOI:https://doi.org/10.1103/PhysRevB.74.205425