Arthur Ayyadurai Moses Ezhil Raj

The effect of post-growth annealing on the phase transformation leading to phase pure hematite (α-Fe₂O₃) nanoparticles is reported in this work. Co-precipitation technique was used to synthesise iron oxide nanoparticles by adjusting the pH of the solution. The xerogel was dried at 80 °C and the obtained powder was calcined in the temperature range 400–800 °C for 3 h. in air. Annealing temperature was prefixed on the basis of the thermal degradation pattern of the starting precursor. X-ray diffraction (XRD) study endorsed the presence of mixed phases FeO, FeO₂ and α-Fe₂O₃ in the as-prepared sample. On annealing, the minor phases transform gradually to α-Fe₂O₃, as confirmed through thermal studies. Performed Rietveld analysis confirms the presence of impurity phases in samples annealed at low temperature. Phase pure sample crystallizes in the rhombohedral corundum structure (space group, R-3c) with a = 5.04044 Å, c = 13.7628 Å and c/a = 2.73048. FT-Raman spectral investigations allowed for a clear assignment of the α-Fe₂O₃ phase. Chemical analysis advocated the only presence of Fe³⁺ ions that octahedrally coordinated with hexagonally close packed O^2- ions that constitute corundum structure. Electron microscopy (TEM) images proved the non-spherical particle distribution in the range 80–100 nm with mean particle size of 93 nm. Structural phase transition with annealing temperature was further confirmed through the fluctuations in the magnetic structure. In analogues to XRD, magnetic study also served as a judging tool to identify purity and the presence of mixed phases in hematite.

Iron oxide nanoparticles were successfully synthesised by a facile solution approach employing iron (III) chloride (FeCl

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