Stabilization of the high coercivity ε-Fe2O3 phase in the CeO2-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 epsilon-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 degrees C, and characterized by the Mossbauer 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 gamma-Fe2O3 phase for the sample with low Fe concentration and low annealing temperature and stabilization of the major epsilon-Fe2O3 phase for high Fe concentration and high annealing temperature, coexisting with the most stable alpha-Fe2O3 a phase. A continuous increase of the particle size of the CeO2 nanocrystals with increasing annealing temperature was also observed. (C) 2012 Elsevier Inc. All rights reserved.