Structural–Transport Properties Relationships on Ce1–xLnxO2−δ System (Ln = Gd, La, Tb, Pr, Eu, Er, Yb, Nd) and Effect of Cobalt Addition

A large series of doped cerias have been prepared by the coprecipitation method combined with impregnation and completely characterized in order to have an overall understanding of the structural, oxygen vacancy concentration, and transport properties relationships. Several lanthanides were incorporated in the fluorite structure, and the effects of the final sintering temperature (1073 and 1573 K) and the addition of cobalt oxide on the structural properties were studied. The chosen lanthanides (Gd, La, Tb, Pr, Eu, Er, Yb and Nd) included a large range of ionic radii and different metals exhibiting variable oxidation states under the typical operating conditions for these materials. The materials have been characterized by powder XRD, high-temperature XRD, micro-Raman spectroscopy, helium pycnometry, and dc conductivity. Transport properties were correlated with structural features induced by the different ionic radii and variable oxidation state of the dopants. The highest ionic conductivity was obtained for the less distorted cells (Gd- and Nd-doped ceria) which represent the optimum balance between Coulomb interactions, steric effects, and vacancy distribution. The lowest Ea value was found for materials with long cell parameters.