Identification of ferric oxide polymorphs in nanoparticles prepared by sol-gel method and maximization of ε-Fe2O3 content

The effects of annealing temperature (1000-1125 °C) and Fe2O3 mass fraction (0.3-0.5) in the initial mixture on the composition of ferric oxide polymorphs within the Fe2O3/SiO2 nanocomposite prepared by sol-gel method were investigated. The structural and magnetic properties of prepared samples were characterized in detail by combination of X-ray powder diffraction (XRPD), high-resolution transmission electron microscopy, magnetic measurements and a local probe technique - transmission Mössbauer spectroscopy (TMS). The optimal conditions for preparation of ε-Fe2O3 rich sample were established and ∼91% of the ε-phase was reached with the characteristic particle diameter of 25 nm. It was observed that with increasing mass fraction of Fe2O3 in the starting material, the optimal annealing temperature decreases, while the width of the particle size distribution tends to increase. The relative concentrations of the four present polymorphs derived from XRD and TMS are in very good mutual agreement.