This study prepared a dense Sm-doped ceria (SDC) and an SDC carbonate composite (abbreviated as SDC-C). The latter was prepared by immersing porous SDC with a formula of (Ce0.8Sm0.2)O1.9 and a relative density of approximately 65-70% into a molten mixture of carbonates containing 1:1 molar ratio of Li2CO3 and Na2CO3 at 500 °C. The relative density of the SDC-C was close to 100%. In addition, SDC oxide without carbonates, which also has a relative density of close to 100%, was heat treated at 1600 °C. At 500 °C, the electrical conductivity and ionic transference number (ti) of the SDC oxide were 1.79(5) × 10−3 S·cm−1 and 0.99(2), respectively, such that electronic conduction could be disregarded. Increasing the temperature caused a gradual decrease in the ti of SDC. Following the addition of carbonates to SDC, the electrical conductivity reached 1.23(9) × 10−1 S·cm−1 at 500 °C. After 14 days (340 h), the electrical conductivity of the SDC-C at 490 °C, leveled off at about 6 × 10−2 S·cm−1. SDC-C could be used as a potential electrolyte in solid oxide fuel cells (SOFCs) at temperatures below 500 °C. ; SCI ; 國內 ; Y ; 電子版 ; GBR