Densification of Sm_0.2Ce_0.8O_1.9 with the addition of lithium oxide as sintering aid

20 mol% samarium doped cerium oxide (Sm_0.2C_0.8O_1.9, SDC) has one of the highest ionic conductivities as electrolyte for solid oxide fuel cell in intermediate temperature, but is restricted to commercial application for its poor densification behavior. The addition of 2 mol% Li₂O in the Sm_0.2Ce_0.8O_1.9 (SDC2) improves its maximum shrinkage rate from 4.6 × 10^-3 min^-1-1.1 min^-1 at a heating rate of 10 °C min^-1. The relative density of SDC2 achieves 99.5% at 898 °C and 3 °C $min^-1, while it is only 82% for SDC at 1250 °C and 3 °C min^-1. The grain boundary diffusion is the densification mechanism, and the mobility of grain boundary increases from 9.8 × 10^-19 m³ N^-1 s^-1 of SDC to 4.2 × 10^-17 m³ N^-1 s^-1 of SDC2 at 900 °C. The activation energy for densification as high as 5.5 ± 0.5 eV for SDC2 contributes to the formation of liquid phase in the grain boundary. The open circuit voltage of the cell using SDC2 as electrolyte as high as 0.78 V at 600 °C under solid oxide fuel cell (SOFC) working conditions demonstrates its promising for SOFC electrolyte.