Abstract
It is difficult to obtain γ-Fe2O3 nanostructures by heating iron substrate in ambient conditions because γ-Fe2O3 is less thermodynamically stable than α-Fe2O3. In this work, we synthesize γ-Fe2O3 nanowires by heating iron particles under an external force. The stacking style of iron and oxygen ions under a strong shearing stress tends to adopt the γ-Fe2O3 structure regardless of the thermodynamic restriction. These γ-Fe2O3 nanowires exhibit a clear ferromagnetic property. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) measurements confirm that γ-phase structure appears only under the applied external force during the heating period. A window of the magnitude of the external force is found to help the nanowire growth on iron particles. The growth mechanism of γ-Fe2O3 nanowires other than α-Fe2O3 under the external force is discussed and an applied stress-assisted growth model is proposed. This work presents an easy approach to produce ferromagnetic iron oxide nanowires on a large scale.
Highlights
Iron oxide nanowires have attracted intensive interest due to their application in gas sensors, catalysts, Li-ion battery, and ferromagnetic contrast agents [1]
By contrast with the flat iron film or foil in previous literature [6,7,8,11,12,13], we choose iron particles as the source and substrate to investigate the effect of the external force on nanowire growth in this work
We call such an extra stress the applied stress and propose that the iron particle as a suitable object to observe the effect of the applied stress on nanowire growth
Summary
Iron oxide nanowires have attracted intensive interest due to their application in gas sensors, catalysts, Li-ion battery, and ferromagnetic contrast agents [1]. The study on Fe2O3 nanowire growth reveals a process determined by the oxidation process of the iron substrate surface. Iron ion diffusion and a grain boundary are two critical conditions for α-Fe2O3 nanowire growth at lower heating temperature.
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