Electronic and ionic conductivity of Eu_0.2Ce_0.8O _2-δ

Eu-doped cerium oxide was synthesized and its crystal structure was analyzed by X-ray diffraction. The electrical conductivity was measured by impedance spectroscopy at 350-900 °C over a wide range of controlled oxygen partial pressures, from H₂ to O₂, using gas mixtures. In the high pO₂ region, ionic conductivity is predominant, and the activation energy for total conductivity is 0.8 ± 0.01 eV. In low pO ₂, the conductivity is found to obey a - 1/4 power law dependence on pO₂, with an enthalpy of reduction of 4.2 ± 0.16 eV. These results demonstrate that Eu has a similar effect on electrical properties as Gd or Sm acceptor dopants in ceria, namely, that Eu shows no evidence for multivalent behavior; rather, it appears to be a fixed valent dopant in the fluorite structured ceria, in contrast to prior studies finding multivalency of Eu in perovskite oxides under similar conditions.