Grain boundary conductivity of high purity neodymium-doped ceria nanosystem with and without the doping of molybdenum oxide

Solid solutions of Ce1−xNdxO2−x/2 (0.05 ≤ x ≤ 0.2) and (Ce1−xNdx)0.95Mo0.05O2−δ (0.05 ≤ x ≤ 0.2) have been synthesized by a modified sol–gel method. Both materials have very low content of SiO2 (~27 ppm). Their structures and ionic conductivities were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and electrochemical impedance spectroscopy (EIS). The XRD patterns indicate that these materials are single phases with a cubic fluorite structure. The powders calcined at 300 °C with a crystal size of 5.7 nm have good sinterability, and the relative density could reach above 96% after being sintered at 1450 °C. With the addition of MoO3, the sintering temperature could be decreased to 1250 °C. Impedance spectroscopy measurement in the temperature range of 250–800 °C indicates that a sharp increase of conductivity is observed when a small amount of Nd2O3 is added into ceria, of which Ce0.85Nd0.15O1.925 (15NDC) shows the highest conductivity. With the addition of a small amount of MoO3, the grain boundary conductivity of 15NDC at 600 °C increases from 2.56 S m−1 to 5.62 S m−1.