Transformation of C$_{70}$ peapods into double walled carbon nanotubes

International audienceX-ray diffraction studies comparing the transformation of C$_{60}$ and C$_{70}$ peapods into double walled carbon nanotubes are presented. The structures of the as-formed DWCNTs are strikingly similar, showing that they are not dependent on the nature of the fullerene precursor. High temperature X-ray diffraction measurements of C$_{70}$ peapods below the coalescence temperature show that confined C$_{70}$ molecules in large tubes undergo an orientational transition to free rotations. Fast re-orientations of C$_{70}$ molecules allow cyclo-addition between adjacent fullerenes to form, in good agreement with the mechanism of coalescence proposed in the literature for C$_{60}$ molecules