Effect of temperature and dopant concentration on the conductivity of samaria-doped ceria electrolyte

The conductivity, sigma, of a samaria-doped ceria electrolyte is studied as a function of temperature and dopant concentration, x, which was from 5 to 30 mol%. It is shown that a maximum in sigma versus x corresponds to a minimum in activation energy. It is found that the conductivity is completely due to oxygen vacancy conduction. The conductivity increases with increasing samaria doping and reaches a maximum for (CeO2)(0.8) (SMO1.5)(0.2), which has a conductivity of 5.6x10(-1) S/cm at 800 degreesC. A curvature at T= T-c, the critical temperature, has been observed in the Arrhenius plot. This phenomenon may be explained by a model which proposed that, below T-c, nucleation of mobile oxygen vacancies into ordered clusters occurs, and, above T-c, all oxygen vacancies appear to be mobile without interaction with dopant cation. In addition, the composition dependences of both the critical temperature and the trapping energy are consistent with that of the activation energy.