Structure and Electrical Properties of MgO or Fe2O3-Doped Ce0.8Nd0.2O1.9 Solid Electrolytes

A precursor powder of Ce0.2Nd0.2O1.9 (NDC) containing 0.05% (mass fraction) SiO2 as an impurity (NDCSi) was doped with 0-2.0% (molar fraction) MgO or FeO1.5 via the sol-gel method. After pressing at 10 MPa, the samples were sintered at 1300 degrees C for 6 h. The structure of the pellets was characterized by X-ray diffraction (XRD), Raman spectroscopy, and field emission scanning electron microscopy (FE-SEM). The electrical conductivity of the pellets was measured using AC impedance spectroscopy. All of the samples exhibited a cubic fluorite structure. Doping with MgO or Fe2O3 lowered the sintering temperature, and increased the density, grain boundaries and total conductivity of NDCSi. The relative density of the samples doped with Fe2O3 or MgO (>93%) was higher than those of NDC or NDCSi (about 86%), suggesting these dopants are effective at promoting densification. NDCSi + 0.5Fe(1.5) and NDCSi + 2.0MgO samples exhibited the highest conductivities of 0.63 x 10(-2) and 0.29 x 10(-2) S . cm(-1), respectively, which are 5.7 and 2.6 times larger than that of NDCSi (0.11 x 10(-2) S . cm(-1)) at 550 degrees C. Doping with MgO or Fe2O3 had a larger effect on the grain boundary conductivity of SDCSi than the bulk conductivity. These results indicate that MgO and Fe2O3 are effective sintering aids as well as grain boundary scavengers with different mechanisms.