| A set of studies on the electrical properties and the ionic conduction in the interfacial regions (i.e. grain boundaries) of fluorite-structured solid electrolytes (SEs) used in solid oxide fuel cells (SOFCs) is presented.;The effects of the introduction of transition metals (TMs) into the grain boundaries, and their concentration on the electrical properties of 1 mol% Gd doped ceria were studied under the space charge model. A reduction of the space charge potential (an intrinsic cause of the blocking effect of grain boundaries to oxygen ionic conduction), and consequently of the grain boundary resistivity, with no modification of the bulk properties was found. An optimum TM concentration exists to have a minimum in grain boundary resistivity.;The grain boundary conductivity of Gd doped ceria and its activation energy as a function of dopant content were studied under the space charge model. The increase of the grain boundary conductivity is inherently due to the decrease in space charge potential as the dopant concentration increases.;The oxygen ion dynamics of Sc doped ceria were also studied via 455Sc MAS NMR, and impedance spectroscopy. For the first time, the oxygen ion dynamics were studied from the analysis of the changes in the coordination sphere of a cation (i.e. Sc) upon temperature via NMR spectroscopy.;In another study, a strong correlation was found between the enthalpy of formation of ceria based materials (i.e., La and Gd doped ceria) and their bulk conductivities. The maxima in these two properties coexist around the same critical dopant content, so that useful information about such concentration for the conductivities can be gained from calorimetric studies and vice versa.;The dependence of low temperature protonic conductivity on grain size (in the ∼ 13 to 100 nm range) of 8 mol % yttria stabilized zirconia (YSZ), was studied. Also, an analysis of the conduction pathway of protons in YSZ based on the impedance spectra responses revealed that grain boundaries are highly selective: they constitute a barrier for oxygen ion conduction, but become the conduction pathway for protons at low temperatures. |
