Pressure-induced phase transitions in iron-filled carbon nanotubes: X-ray diffraction studies

Abstract

High-pressure x-ray-diffraction studies have been carried out upto 20 GPa on iron-filled multiwalled carbon nanotubes (MWNTs). The pressure dependence of the intertubular spacing ${d}_{0}$ of the filled MWNTs shows a sharp change at 9 GPa which is not observed in pristine MWNTs. The iron present as nanowires inside the MWNT is in the form of \ensuremath{\alpha}-Fe and ${\mathrm{Fe}}_{3}\mathrm{C}.$ Both of these phases show higher compressibility than their bulk form. Most interestingly, the structural modification of MWNTs at 9 GPa coincides with an iso-structural phase transition in the encapsulated ${\mathrm{Fe}}_{3}\mathrm{C},$ in sharp contrast to the absence of a transition in the bulk ${\mathrm{Fe}}_{3}\mathrm{C}$ upto 70 GPa.