Defect structures in doped CeO2 studied by using XAFS spectrometry

The local structures around Ce and Ln atoms in Ce1−xLnxO2−x/2 (Ln=Sc, Y, Nd, Sm, Gd, Yb, x=0–0.30) were studied by using EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) spectroscopy. The oxidation state of Ce was found to be present predominantly as the tetravalent Ce4+ cations in all Ce1−xLnxO2−x/2 samples. Except for the Ce–O distances in Sc-doped CeO2 showing the presence of two-phase of Sc2O3 and Ce1−xScxO2−x/2, the Ce–O distances in Ce1−xLnxO2−x/2 were seen to decrease with increasing dopant concentration, suggesting that oxygen vacancies introduced by doping trivalent cations Ln to CeO2 were thought to be located around Ce ions. With dopant content, the Gd–O distances decreased but Y–O distances were seen almost constant. Several complex defect structures composed of Ce, Gd or Y and oxygen atoms were proposed.