The microstructures and property analysis of aliovalent cations (Sm3+, Mg2+, Ca2+, Sr2+, Ba2+) co-doped ceria-base electrolytes after an aging treatment

Ce0.8Sm0.15R0.05O2−δ (R = Sm, Mg, Ca, Sr, and Ba) specimens were successfully prepared using a solid-state reaction, and they were used in an intermediate temperate solid oxide fuel cell (IT-SOFC) electrolyte. This study focused on the effects of co-doping and an aging treatment for the conductivities and microstructures of CeO2-based ceramics and also analyzed the variation of the conductivity in the reducing atmosphere. The study showed that the conductivities of the CeO2-based materials have a higher conductivity at 500–800 °C by the co-doping aliovalent cations Sm and R. The conductivity increased with the increasing oxygen vacancies that were induced from charge compensation. The XRD and EDS analyses showed that the MgO and BaCeO3 phases appeared in the Ce0.8Sm0.15Mg0.05O2−δ and Ce0.8Sm0.15Ba0.05O2−δ specimens, respectively. The conductivity of the Ce0.8Sm0.15Ca0.05O2−δ specimens was higher, approximately 0.0837 S/cm at 800 °C in the air. The thermal expansion coefficient (TEC) in all samples was ca. 11–15 × 10−6/°C at 200–800 °C. After an aging treatment at 700 °C for a holding time of 1000 h, the conductivities of all samples showed almost no change. However, the conductivity in Ce0.8Sm0.15Ca0.05O2−δ decreased from 0.0837 to 0.0581 S/cm, and the grain size increased. The conductivities of the CeO2-based specimens were also measured under a 5%H2–95%N2 atmosphere, and the conductivity greatly increased in the reducing atmosphere because the Ce4+ ions reduced to Ce3+ ions.