We have examined the crystal structures, surface textures, oxygen mobility, oxygen storage capacity, and redox behaviors of Re0.6Zr0.4-xYxO2 (RE = Ce, Pr; x = 0, 0.05) solid solutions. According to the results of X-ray diffraction (XRD) studies, there are two cubic phases (Ce0.75Zr0.25O2, major; ZrO1.87, minor) in Ce0.6Zr0.4O2 (denoted as CZ hereafter) and Ce0.6Zr0.35 Y0.05O2 (CZY), but only one cubic phase in Pr0.60Zr0.40O2 (PZ) and Pr0.60Zr0.35 Y0.05O2 (PZY). These nanosized materials are porous and have large surface areas. As revealed by the Cc 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 H-2 (or CO)-O-2 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 O-18/O-16 exchange studies show that, with the presence of oxygen vacancies, the lattice O2- mobility on/in CZY and PZY enhanced. Based on such outcomes, we conclude that, by incorporating Y3+ 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. (C) 2003 Elsevier B.V. All rights reserved.