Structure and Oxide Ion Conductivity: Local Order, Defect Interactions and Grain Boundary Effects in Acceptor-Doped Ceria

The long-range and short-range structure of nanocrystalline and microcrystalline acceptor-doped ceria is investigated by a combined approach using EXAFS, XANES, Raman, and XRD, and correlated with the oxide-ion conductivity in the bulk and in grain boundaries. Compared to Yb3+ and Er3+, the positive influence of Sm3+ is attributed to the ability to repel oxygen vacancies, and to keep a localized disorder around the dopant. The long-range structural analysis shows lattice contraction for Yb- and Er-doping and lattice expansion for Sm-doping. The short-range analysis around the dopants and cerium highlights that a more complex structural rearrangement has to be assumed to explain the complementary results of the different techniques. Nominally trivalent dopants are also shown to have an effect on the electronic structure of ceria, and the consequences on oxide-ion conductivity are highlighted.