Apparent non-monotonic electrical conductivity relaxation of 1 % Gd-doped ceria

Steady-state and transient electrical conductivities of 1 % Gd-substituted ceria have been characterized from 550 to 800 °C under oxidizing conditions. The temperature and oxygen pressure dependencies of the steady-state conductivity resemble those of pristine ceria, with predominant n-type conductivity and some contribution of p-type conductivity under the most oxidizing conditions. Depending on temperature and oxygen partial pressure, the relaxation of the conductivity follows one-fold monotonic, two-fold monotonic, or non-monotonic behavior, despite the predominance of two charge carriers in the bulk material. Possible explanations for this peculiar phenomenon are discussed based on surface-exchange-limited oxygen exchange. • 1 % Gd doping is used to probe and extrapolate the oxygen exchange kinetics of nominally pristine ceria. • Steady-state conductivity of 1GDC revels p-type conductivity under atmospheric conditions. • ECR measurements show both monotonic and non-monotonic relaxation behaviors in 1GDC. • Monotonic relaxation transitions to non-monotonic behavior with increasing temperature and decreasing pO 2 . • Reestablishment of the space charge layer is proposed to explain the relaxation behavior.