Synthesis and characterization of cerium substituted hematite by sol–gel method

Fine particles of cerium substituted hematite with different compositions were prepared by the sol–gel method from the aqueous solution of their corresponding metal salts. Mixed hydroxides of Fe3+ and Ce4+ were obtained by reacting aqueous NH3 with the aqueous solution of FeCl3 and Ce(NH3)2(NO3)6 at pH 2.5–3.0) and they were heat treated at different temperatures between 400 and 1200 °C in air for 2 h to get the mixed oxide product. Thermal analysis and X-ray diffraction studies revealed the coexistence of Fe2O3 and CeO2 phase separately up to 900 °C, and covalent interaction between them above 1000 °C, which was evidenced by the shifting of the XRD peaks. Unit cell parameters and the cell volumes (V) of the samples derived between 1000 and 1200 °C were found to be in the range a = 5.045–5.048 ± 0.007 Å, c = 13.774–13.815 ± 0.041 Å and V = 303.608–304.874 Å3 respectively. It was observed that both the lattice parameters and the cell volumes were higher than that of the pure α-Fe2O3 (a = 5.036 Å, c = 13.749 Å, V = 301.976 Å3) system. The expansion of lattice parameters further supported the incorporation of the large Ce4+ ion into the α-Fe2O3 matrix. The lattice parameter increased with increasing Ce4+ ion loading. FESEM studies showed the growth of the particles with increasing temperature though it was suppressed due to the presence of Ce4+ ions as compared to the pure system.