Effect of Fe₂O₃ on Sm-doped ceria system solid electrolyte for IT-SOFCs

The effect of Fe₂O₃ addition (0-2.5 mol%) on the densification, crystal structure, ionic conductivity, and aging behavior of Ce_0.8Sm_0.2O_1.9 (SDC) was studied. The addition of Fe₂O₃ promotes densification, reducing sintering temperature by ∼100-150 °C. X-ray diffraction showed that these materials exhibit a fluorite structure; a second phase of Fe₂O ₃ is identified when Fe₂O₃ content was ≥1.5 mol%. Impedance spectroscopy measurements indicated that SDC with 0.25 mol% Fe₂O₃ has the highest conductivity, about 10% higher than that of SDC at 700 °C. Conversely, a reduction in conductivity is observed in all samples after aging in air at 800 °C for 120 h. Because of the harmful effect of aging, conductivity rapidly decreases as Fe₂O ₃ content in the samples exceeded 0.25 mol%. However, SDC with 0.25 mol% Fe₂O₃ shows the same magnitude of decrease in conductivity compared with that of SDC after aging. This indicates that SDC with 0.25 mol% Fe₂O₃ continues to present the best conductivity even after high-temperature aging.