RE_0.6Zr_0.4-xY_xO₂ (RE = Ce, Pr; X = 0, 0.05) solid solutions: An investigation on defective structure, oxygen mobility, oxygen storage capacity, and redox properties

We have examined the crystal structures, surface textures, oxygen mobility, oxygen storage capacity, and redox behaviors of RE_0.6Zr _0.4-xY_xO₂ (RE=Ce, Pr; x=0, 0.05) solid solutions. According to the results of X-ray diffraction (XRD) studies, there are two cubic phases (Ce_0.75Zr_0.25O₂, major; ZrO_1.87, minor) in Ce_0.6Zr_0.4O₂ (denoted as CZ hereafter) and Ce_0.6Zr_0.35Y _0.05O₂ (CZY), but only one cubic phase in Pr _0.60Zr_0.40O₂ (PZ) and Pr_0.60Zr _0.35Y_0.05O₂ (PZY). These nanosized materials are porous and have large surface areas. As revealed by the Ce 3d and Pr 3d results of X-ray photoelectron spectroscopic (XPS) investigations, the doping of Y³⁺ ions into the CZ and PZ lattices resulted in an increase in concentration of oxygen vacancies and Ce³⁺ and Pr⁴⁺ ions. The results of H₂ (or CO)-O₂ titration and temperature-programmed reduction (TPR)-reoxidation experiments indicate the presence of a reversible redox behavior of Ce⁴⁺/Ce³⁺ in CZY and Pr⁴⁺/Pr³⁺ in PZY. The results of ¹⁸O/¹⁶O exchange studies show that, with the presence of oxygen vacancies, the lattice O^2- mobility on/in CZY and PZY enhanced. Based on such outcomes, we conclude that, by incorporating Y ³⁺ ions into CZ and PZ, one can enhance (i) lattice oxygen mobility, (ii) Ce³⁺ and Pr⁴⁺ concentrations, and (iii) oxygen uptake capacity. We observed that PZY is superior to CZY in redox behavior, oxygen mobility, and oxygen storage capacity.