Reduction behaviour in neodymium doped ceria

Doped cerium oxides are technologically relevant materials and used as electrolytes in intermediate temperature solid oxide fuel cells. An important issue for these materials is the reduction of ceria at low oxygen partial pressures which leads to mixed ionic electronic conduction. In the present work, reduction behaviour in Ce0.8Nd0.2O1.9-δ is examined under inert and strongly reducing conditions. Even under inert conditions, ca. 3.5 % of the Ce is redox active up to around 800 °C, which appears to be correlated with non-linear behaviour in the Arrhenius plot of conductivity and thermal expansion of the lattice. Under more strongly reducing conditions, a secondary partial reduced phase is formed related to triclinic Ce11O20, which introduces significant electronic conductivity into the system. The dynamics of the re-oxidation process are examined using X-ray powder diffraction and electrochemical impedance spectroscopy.