Evaluation of Li2O as an efficient sintering aid for gadolinia-doped ceria electrolyte for solid oxide fuel cells

Li2O has been evaluated as a sintering aid for Gd0.1Ce0.9O2−δ (GDC). Using 2.5 mol% ratio of Li2O to GDC (5LiGDC), dense samples with relative density of 99.3% were achieved at sintering temperature as low as 900 °C. A high total conductivity of 0.059 S cm−1 at 600 °C was obtained for the 5LiGDC samples sintered at 1000 °C (5LiGDC1000), while 5LiGDC samples sintered at 1400 °C showed a lower conductivity of 0.017 S cm−1 at 600 °C. It has been found that Li2O has the tendency to accumulate in the grain boundary region to form Li-Gd-Ce-O phases when the 5LiGDC sintering temperature is at 1000 °C or below, leading to an increase in the grain boundary conductivity. Increasing the 5LiGDC sintering temperature above 1000 °C will accelerate the vaporization of Li2O, association of the oxygen vacancy and formation of additional pores in the bulk, resulting in a decrease of both the grain boundary and grain interior conductivity. Secondary ion mass spectrometry (SIMS) results have confirmed the existence of Li ions for the 5LiGDC samples sintered at or below 1000 °C, while most of Li species has vaporized for the 5LiGDC samples sintered above 1000 °C.