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 ͑MWNTs͒. 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 ␣-Fe and Fe 3 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 Fe 3 C, in sharp contrast to the absence of a transition in the bulk Fe 3 C upto 70 GPa.

Pressure-induced phase transitions in cobalt-filled multiwalled carbon nanotubes

“…3, beyond 9 GPa the full width at half maximum ͑FWHM͒ of the MWCNT Bragg peak begins increasing, a feature similar to what has been observed for the pristine tubes by us and others. 12,24 This has been ascribed to partial disorder or heterogeneous deformation of the tubes. It should be noted that the observed increase of the FWHM of the MWCNT peak is not due to the nonhydrostatic stresses, as can be inferred from the comparison of the FWHM of the MWCNT peak with that of the gold pressure calibrant, also given in Fig.…”

“…10 In fact, materials, when encapsulated inside carbon nanotubes, show interesting physical and structural properties that could be much different than their bulk counterparts. 11,12 Our previous high-pressure structural investigations on iron-filled carbon nanotubes showed several remarkable features of nanowires and the nanotubes. 12 High-pressure structural studies showed that the filled mutiwalled carbon nanotubes, unlike pristine tubes, show sudden polygonization at a pressure at which the interfacial part of the nanowires ͑Fe 3 C͒ also underwent an isostructural phase transition.…”

“…11,12 Our previous high-pressure structural investigations on iron-filled carbon nanotubes showed several remarkable features of nanowires and the nanotubes. 12 High-pressure structural studies showed that the filled mutiwalled carbon nanotubes, unlike pristine tubes, show sudden polygonization at a pressure at which the interfacial part of the nanowires ͑Fe 3 C͒ also underwent an isostructural phase transition. As both transitions occur at the same pressure, the transformation mechanism remained unclear.…”

Comparative high pressure Raman study of boron nitride nanotubes and hexagonal boron nitride

“…The fact that the linewidth gets broadened with increasing pressure and the Raman signature disappears, we believe that the BN multi-walled nanotube becomes amorphous after 12 GPa and hence it does not recover on decompression. The pressure effects on carbon multi-walled nanotubes (CMWNTs) are seen to be reversible upto 20 GPa [15]. X-ray diffraction experiments show that C-MWNTs become irreversibly amorphous after ~ 51 GPa [16].…”

Structural and Electronic Properties of Lithium Nanowires

“…Чаще всего рассматривались нанопровода металлов, находящиеся внутри углеродных или иных нанотрубок. Конечно же, основное современ-ное направление исследований -нанопровода переходных метал-лов [6][7][8], но и щелочные металлы представляют, безусловно, нема-лый интерес. Так, например, заполнение калием углеродной нано-трубки увеличивает проводимость в ней в 20-30 раз [9], т.е.…”