Stabilization of the high coercivity ϵ-Fe2O3ϵ-Fe2O3 phase in the CeO2–Fe2O3/SiO2CeO2–Fe2O3/SiO2 nanocomposites

We have investigated the processes leading to the formation of the Fe2O3 and CeO2 nanoparticles in the SiO2 matrix in order to stabilize the ϵ-Fe2O3ϵ-Fe2O3 as the major phase. The samples with two different concentrations of the Fe were prepared by sol–gel method, subsequently annealed at different temperatures up to 1100 °C, and characterized by the Mössbauer spectroscopy, Transmission Electron Microscopy (TEM), Powder X-ray Diffraction (PXRD), Energy Dispersive X-ray analysis (EDX) and magnetic measurements. The evolution of the different Fe2O3 phases under various conditions of preparation was investigated, starting with the preferential appearance of the γ-Fe2O3γ-Fe2O3 phase for the sample with low Fe concentration and low annealing temperature and stabilization of the major ϵ-Fe2O3ϵ-Fe2O3 phase for high Fe concentration and high annealing temperature, coexisting with the most stable α-Fe2O3α-Fe2O3 phase. A continuous increase of the particle size of the CeO2 nanocrystals with increasing annealing temperature was also observed.

The graphical abstract displays the most important results of our work. The significant change of the phase composition due to the variation of preparation conditions is demonstrated. As a result, significant change of the magnetic properties from superparamagnetic γ-Fe2O3γ-Fe2O3 phase with negligible coercivity to the high coercivity ϵ-Fe2O3ϵ-Fe2O3 phase has been observed.Figure optionsDownload as PowerPoint slideHighlights
► Research of the stabilization of the high coercivity ϵ-Fe2O3ϵ-Fe2O3 in CeO2–Fe2O3/SiO2.
► Samples with two different concentrations of Fe and three annealing temperatures.
► Phase transition γ→ϵ→(β)→αγ→ϵ→(β)→α with increasing annealing temperature and particle size.
► Elimination of the superparamagnetic phases in samples with higher content of Fe.
► Best conditions for high coercivity ϵ-Fe2O3ϵ-Fe2O3—higher Fe content and TA=1100°C.