The physical and chemical properties of bulk Ce 1Ϫx Tb x O 2 and Ce 1Ϫx Tb x O y nanoparticles (x р0.5) were investigated using synchrotron-based x-ray diffraction ͑XRD͒, x-ray adsorption near edge spectroscopy ͑XANES͒, Raman spectroscopy ͑RS͒, and first-principles density-functional ͑DF͒ calculations. DF results and Raman spectra point to a small tetragonal distortion after introducing terbium in ceria. The results of XRD show a small contraction ͑р 0.08 Å͒ in the cell dimensions. The presence

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... of Tb generates strain in the lattice through the variation of the ionic radii and creation of crystal imperfections and O vacancies. The strain increases with the content of Tb and affects the chemical reactivity of the Ce 1Ϫx Tb x O y nanoparticles towards hydrogen, SO 2 , and NO 2 . DF calculations for bulk Ce 1Ϫx Tb x O 2 and Ce 8Ϫn Tb n O 16 (nϭ0, 1, 2, or 4͒ clusters show oxide systems that are not fully ionic. The theoretical results and XANES spectra indicate that neither a Ce↔Tb exchange nor the introduction of oxygen vacancies in Ce 1Ϫx Tb x O y significantly affect the charge on the Ce cations. In contrast, the O K-edge and Tb L III -edge XANES spectra for Ce 1Ϫx Tb x O y nanoparticles show substantial changes with respect to the corresponding spectra of Ce and Tb single oxide references. The Ce 0.5 Tb 0.5 O y compounds exhibit a much larger Tb 3ϩ /Tb 4ϩ ratio than TbO 1.7 . A comparison with the properties of Ce 1Ϫx Zr x O y and Ce 1Ϫx Ca x O y shows important differences in the charge distribution, the magnitude of the dopant induced strain in the oxide lattice, and a superior behavior in the case of the Ce 1Ϫx Tb x O y systems. The Tb-containing oxides combine stability at high temperature against phase segregation and a reasonable concentration of O vacancies, making them attractive for chemical and catalytic applications.