Influences of Gd2Ti2O7 sintering aid on the densification, ionic conductivity and thermal expansion of Gd0.1Ce0.9O1.95 electrolyte for solid oxide fuel cells

Abstract The effects of Gd 2 Ti 2 O 7 (GT) as sintering aid on the densification, electrical properties and thermal expansion of Gd 0.1 Ce 0.9 O 1.95 (GDC) are examined. Samples added with TiO 2 sintering aid are also tested for comparison. It is found that by sintering at a moderate temperature of 1400 °C for 5 h, the relative density of the GT-added GDC can reach over 97% as the molar ratio of GT/GDC reaches 0.02 or higher. XRD analysis indicates that GT does not react with GDC, while TiO 2 reacts with Gd in GDC to form GT. The ionic conductivities of the GT-added and the TiO 2 -added GDC are analyzed by AC impedance spectroscopy at 500–700 °C. The result shows that although the ionic conductivity of the GT-added GDC decreases as the GT/GDC molar ratio increases up to 0.05, it is still higher than that of 8YSZ and much higher than that of the GDC added with an equivalent amount of TiO 2 . It is also found that the thermal expansion coefficient of GDC decreases as the amount of GT increases. These results show that GT is an excellent sintering aid for GDC, and the optimal molar ratio of GT/GDC is 0.02 in terms of densification and ionic conductivity.