Structure, morphology and electrical conductivity of Sm and Bi co-doped CeO₂ electrolytes synthesized by co-precipitation method

In this paper, explain a new relationships between Bi³⁺ content, the phase crystal, microstructure and conductivity for Sm and Bi co-doped Ce_0.8−xSm_0.2Bi_xO_1.9−1/2x (x = 0, 0.05, 0.1, 0.15, 0.2) electrolytes prepared by co-precipitation method. The XRD patterns showed that this compounds exhibit a fluorite-type cubic structure after the samples calcined at 700 °C for 4 h and the cell volumes of increased when the Bi content increased. In addition, for the samples sintered at 1400 °C for 4 h, the Bi doping improves the relative density, the grain size and the average thermal expansion coefficient (TEC). More in details, the relative density and TEC increase with the Bi content. Form the AC impedance spectroscopy measurements, the conductivity of the sintered samples is found to improve with the increasing of Bi content (for x ≤ 0.15), which is ascribed to the increasing of the number of oxygen ion vacancies and the increase in the unit cell volume. However, the conductivity decreases when the Bi content is further increased (0.15 < x ≤ 0.2), which is ascribed the reduction of the number of free oxygen vacancies. The highest conductivity at 800 °C is 5.6 × 10⁻² S/cm and the activation energy is 0.83 eV for Ce_0.65Sm_0.2Bi_0.15O_1.825, indicating that this would be a promising electrolyte for the intermediate temperature-solid oxide fuel cell applications.