Nanocrystalline Ce1-xLuxO2-x/2 (x = 0.17, 0.25, 0.5) mixed oxides with narrow size distribution (4-5 nm) were prepared by a water-in-oil (W/O) microemulsion method. Microstructure and reduction-reoxidation properties of the oxides were analyzed by HRTEM, STEM-EDX, XRD, H-2-TPR and TPO. The presence of LU3+ ion in the cation sublattice generates strain in the ceria lattice through the creation of crystal imperfections and oxygen vacancies and drastically affects redox properties of the system. All synthesized samples had fluorite structure of CeO2 from XRD and all exhibited significant, low temperature reducibility (max. at 368 degrees C) persisting after repeated reduction and low temperature oxidation cycles at 500 degrees C. Oxidation treatment at higher temperature (950 degrees C) destroyed completely the low temperature reducibility of the mixed oxides, that could not be accounted for to particle growth. TPO data indicated that Ce3+ species formed after reduction at 930 degrees C in the Ce0.83Lu0.17O1.915 and Ce0.75Lu0.25O1.875 samples were very sensitive to oxygen atmosphere even at room temperature. However, some Ce3+ species formed in the Ce0.5Lu0.5O1.75 sample were very stable in air. Additionally, the existence of biphasic region (F + C) was also unequivocally detected by HRTEM and TPO method in nanocrystalline Ce0.5Lu0.5O1.75 after oxidation treatment at 950 degrees C. (C) 2009 Elsevier B.V. All rights reserved.