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Título : The behavior of mixed-metal oxides: Physical and chemical properties of bulk Ce1–xTbxO2 and nanoparticles of Ce1–xTbxOy
Autor : Wang, Xianqin, Hanson, Jonathan C., Liu, Gang, Rodríguez, José A., Iglesias Juez, Ana, Fernández García, Marcos
Palabras clave : Nanoparticles
Crystal defects
Vacancies (crystal)
Raman spectra
X-ray diffraction
Density functional theory
Fecha de publicación : 15-Sep-2004
Editor: American Institute of Physics
Resumen: The physical and chemical properties of bulk Ce1–xTbxO2 and Ce1–xTbxOy nanoparticles (x<0.5) were investigated using synchrotron-based x-ray diffraction (XRD), x-ray adsorption near edge spectroscopy (XANES), Raman spectroscopy (RS), and first-principles density-functional (DF) 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 ( <0.08 Å) in the cell dimensions. The presence 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 Ce1–xTbxOy nanoparticles towards hydrogen, SO2, and NO2. DF calculations for bulk Ce1–xTbxO2 and Ce8–nTbnO16 (n = 0, 1, 2, or 4) clusters show oxide systems that are not fully ionic. The theoretical results and XANES spectra indicate that neither a CeTb exchange nor the introduction of oxygen vacancies in Ce1–xTbxOy significantly affect the charge on the Ce cations. In contrast, the O K-edge and Tb LIII-edge XANES spectra for Ce1–xTbxOy nanoparticles show substantial changes with respect to the corresponding spectra of Ce and Tb single oxide references. The Ce0.5Tb0.5Oy compounds exhibit a much larger Tb3+/Tb4+ ratio than TbO1.7. A comparison with the properties of Ce1–xZrxOy and Ce1–xCaxOy 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 Ce1–xTbxOy 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.
Descripción : 11 pages, 12 figures, 3 tables.-- PACS: 61.46.+w; 61.72.Ji; 78.70.Dm; 78.30.Hv; 71.15.Mb; 64.75.+g; 82.65.+r
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ISSN: 0021-9606
DOI: 10.1063/1.1781116
Citación : Journal of Chemical Physics 121(11): 5434 (2004)
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