Journal
RSC ADVANCES
Volume 7, Issue 40, Pages 25025-25030Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c7ra03144k
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Funding
- National Natural Science Foundation of China [11404227]
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One of the challenges in the field of carbon nanotubes (CNTs) is the encapsulation of a single crystalline phase of ferromagnetic alpha-Fe. The formation of additional gamma-Fe and Fe3C phases during CNT-growth generally limits the direct encapsulation of these crystals in the form of a single phase. A solution, the use of post-synthesis annealing, has been considered; however oxidation of the encapsulated metal-phases is commonly found due to the elevated temperatures (T) necessary for the phase-conversion. Here we investigate the dynamics of g-Fe to alpha-Fe transition by T-dependent X-ray diffraction in vacuum. We show that a direct gamma-Fe to alpha-Fe transition is present already below 200 degrees C and becomes significantly fast in the T-range of 300-399 degrees C. In such a T-range no metal oxidation is found. Rietveld refinement analyses also show that a T-dependent increase in the unit-cell c-axis value of the graphitic CNT-walls is present.
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