Investigation of ionic conductivities of CeO2-based electrolytes with controlled oxygen vacancies

Effects of Gd2O3 and SrO co-dopants on microstructural features, ionic conductivities and oxygen vacancy concentrations of two modified CeO2 electrolytes (Ce0.8Gd0.2−xSrxO1.9−0.5x and Ce0.8−xGd0.2SrxO1.9−x) are investigated using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and AC impedance spectroscopy. Lattice parameters of co-doped CeO2 specimens are observed to linearly increase with an increase of co-dopants amount, due to larger radius of Sr2+. Grain size of Ce0.8−xGd0.2SrxO1.9−x is significantly larger than that of Ce0.8Gd0.2−xSrxO1.9−0.5x at the same Sr2+ concentration, because Ce0.8−xGd0.2SrxO1.9−x possesses more oxygen vacancy to migrate oxygen ions, defects and impurities easily, based upon calculation of oxygen vacancy amount. Small addition of SrO into 20 mol% Gd2O3 doped CeO2 (Ce0.8−xGd0.2SrxO1.9−x) is effective in enhancing of ionic conductivity, but a sudden decreasing of conductivity with Sr2+ heavy-doping is found. The relationship among co-dopant concentration, oxygen vacancy radius, average binding energy and ionic conductivity in two different co-doped CeO2 systems are discussed in this work.