Low Temperature Combustion Synthesis and Characterization of Pr-CeO<sub>2</sub> Doped with Zr Red Ceramic Pigments

Abstract

New inorganic pigments Ce0.95ZrxPr0.05-xO2(x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) based on CeO2-ZrO2-Pr6O11solid solutions were synthesized by low-temperature combustion synthesis (LCS) method using citric acid as a reductant and metal nitrate as an oxidant. The pigments are CeO2solid solutions doped with praseodymium and zirconium ions, and display colors ranging from dark brown via brick red to bright cream. The prepared pigments were characterized by X-ray powder diffraction, transmission electron microscopy, ultraviolet-visible absorption spectroscopy and colorimetrical measurements. Results show that cubic fluorite structure solid solution of 100 nm Ce0.95ZrxPr0.05-xO2particles can be obtained at 1000 °C. There was an effective absorption of visible blue and green in 600 nm, which is originated from the shift of charge transfer band in CeO2by doping of zirconium and praseodymium ions. Effective red hue was obtained for Ce0.95Zr0.02Pr0.03O2composition, which exhibited better L*, a*,and b* values (57.64, 23.83 and 23.78). The coloring mechanism is based on the introduction of an additional electronic energy level of unpaired 4f electron of the lanthanide ion into the cerianite forbidden band. Furthermore, the doping of Zr in Pr-CeO2system raises the slope of the absorption edge with a blue shift resulting in enhanced lightness. The prepared pigments were prospective to be alternatives for toxic pigments used in coloration of plastics.