Synthesis and characterization of Fe 3+ doped cerium–praseodymium oxide pigments

Inorganic pigments based on (0.95−x)CeO2.(0.05)Pr6O11.(x)α-Fe2O3 (x = 0.00; 0.01; 0.02; 0.03 and 0.04) were synthesized by the solid state reaction method at 1300 °C for 3 h, and the modified sol–gel method at 900 °C for 3 h. The pigments obtained were characterized by X-ray diffraction, 57Fe Mössbauer spectroscopy and UV–Vis reflectance spectroscopy, with determination of colorimetric parameters and band gap. In the X-ray diffraction analysis, diffraction peaks related to the PrFeO3 secondary phase were observed, in the 1–4 mol% α-Fe2O3 doping systems prepared through the solid state reaction. While in the systems synthesized by the modified sol–gel method, only peaks related to the main phase, cerianite, were observed, in 0–3 mol% α-Fe2O3 doping; and the sample with 4 mol% α-Fe2O3 presented the secondary phase PrFeO3. The 57Fe Mössbauer spectroscopy analysis revealed that the sample with 3 mol% α-Fe2O3, synthesized by the modified sol–gel method presented almost all iron ions incorporated within the lattice, while the samples with 4 mol% α-Fe2O3, synthesized by the modified sol–gel method and 3 and 4 mol% α-Fe2O3, synthesized by the solid state reaction method presented hematite signals, together with Fe3+ signals within the cerium or praseodymium oxide lattice. The addition of dopants (Fe3+ and Pr3+/4+) to the CeO2 lattice, even in small proportion, caused distortions in the lattice, decreasing the band gap value, thus allowing energetic absorptions within the visible region. The pigments presented shades ranging from light to dark-brown.