The structural and electronic properties of nanostructured Ce1−x−yZrxTbyO2 ternary oxides: Unusual concentration of Tb3+ and metal↔oxygen↔metal interactions

Abstract

Ceria-based ternary oxides are widely used in many areas of chemistry, physics, and materials science. Synchrotron-based time-resolved x-ray diffraction, x-ray absorption near-edge spectroscopy (XANES), Raman spectroscopy, and density-functional calculations were used to study the structural and electronic properties of Ce-Zr-Tb oxide nanoparticles. The nanoparticles were synthesized following a novel microemulsion method and had sizes in the range of 4-7 nm. The Ce1-x-yZrxTbyO2 ternary systems exhibit a complex behavior that cannot be predicted as a simple extrapolation of the properties of Ce1-xZrxO2, Ce1-xTbxO2, or the individual oxides (CeO2, ZrO2, and TbO2). The doping of ceria with Zr and Tb induces a decrease in the unit cell, but there are large positive deviations with respect to the cell parameters predicted by Vegard's rule for ideal solid solutions. The presence of Zr and Tb generates strain in the ceria lattice through the creation of crystal imperfections and O vacancies. The O K-edge and Tb LIII-edge XANES spectra for the Ce1-x-yZrxTbyO2 nanoparticles point to the existence of distinctive electronic properties. In Ce1-x-yZrxTbyO2 there is an unexpected high concentration of Tb3+, which is not seen in TbO2 or Ce1-xTbxO2 and enhances the chemical reactivity of the ternary oxide. Tb<-->O<-->Zr interactions produce a stabilization of the Tb(4f,5d) states that is responsible for the high concentration of Tb(3+) cations. The behavior of Ce1-x-yZrxTbyO2 illustrates how important can be metal<-->oxygen<-->metal interactions for determining the structural, electronic, and chemical properties of a ternary oxide.