Synthesis and characterization of reddish ceramic pigments based on Y2Ce2O7 co-doped with Pr4+ and Zn2+

Abstract

This research focuses on the analysis and comparison of the effect between Pr doping of yttrium cerate Y2Ce2O7 (Pr series) and Pr- and Zn- co-doping of the same reference compound (Zn series). With this objective, 9 different solid solutions were prepared by means of an ammonia coprecipitation route: the reference compound Y2Ce2O7 (x=0), Y2Ce2-xPrxO7 (x=0.05, 0.10, 0.15, 0.30) which we will call Pr series and Y2-2xCe2PrxZnxO7 (x=0.05, 0.10, 0.15, 0.30) called Zn series. The precipitates formed by the stove-dried precursors were carbonized at 500ºC and later calcined at 1000 and 1200ºC. From the powders at different temperatures, they were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and semiquantitative analysis of energy dispersive X-rays (EDX), optical spectroscopy (UV-VIS-NIR), CIE-L*a*b* colorimetry and finally solar reflectance measurements. The XRD patterns confirmed the successful formation and crystallization of solid solutions prepared with mostly defective fluorite structures accompanied by a small amount of ordered phase type C. As for the optical properties, the evaluation by UV-VIS-NIR spectroscopy clearly shows the effect of the doping on the reference compound, since the doped compounds present displaced bands. This displacement is due to the introduction of additional 4f1 levels of Pr between the 2p band of oxygen and the Ce4+ conduction band, which produces a considerable decrease in the bandgap with respect to the reference compound. The colorimetric measurements show us that the a* component remains practically constant as a function of the variation in the concentration of doping agents, while the b* component decreases slightly as the concentration increases in both series. It is remarkable that both components show a significant decrease when x=0.30 in both series. Regarding solar reflectivity, it should be noted that most compositions show slightly higher values of %R in the series with Zn, except in the composition x=0.30, where it decreases.