Local stabilization of body-centred tetragonal Fe and enhanced dislocation density in carbon nanotubes filled with μm-long nanowires

Abstract

The recent identification of superconductive effects in multilayer graphene systems exhibiting coexistence of rhombohedral and Bernal structural phases has attracted great attention. Complex effects have been reported in the presence of dislocations and/or solitons between graphene layers. Local magnetic fields and percolative effects have also been identified in the presence of wrinkling and disclinations. Interestingly, a recent report has also demonstrated the local stabilization of disorder-rich rhombohedral phases in low dimensional systems comprising of multiwalled carbon nanotubes modified with sulfur. In this work we identify a variation in the predicted ABA Bernal graphitic ordering of multiwalled carbon nanotubes (CNTs) fabricated in the presence of dichlorobenzene as a growth-promoter. The presented results highlight the stabilization of a high density of dislocations in samples produced by pyrolysis of low concentrations of ferrocene. We present an in-depth investigation of the dislocation-rich interfaces, especially by employing HRTEM analyses, evidencing a spontaneous local-insertion of low-dimensional atomic-lines (or solitons) into neighbouring atomic layers of curved graphene. Furthermore, by employing a methodology involving highly controllable cooling-rates and subsequential characterization through X-ray diffraction (XRD), we demonstrate a rapid migration of interstitial carbon, with relaxation of Fe₃C into α-Fe and stabilization of local body centred tetragonal phases within the body centred cubic lattice of the nanowires.