Reducing the operation temperature of solid oxide fuel cells is a major challenge towards their widespread use for power generation. This has triggered an intense materials research effort involving the search for novel electrolytes with higher ionic conductivity near room temperature. Two main directions are being currently followed: the use of doping strategies for the synthesis of new bulk materials and the implementation of nanotechnology routes for the fabrication of artificial nanostructures with improved properties. In this paper, we review our recent work on solid oxide fuel cell electrolyte materials in these two directions, with special emphasis on the importance of disorder and reduced dimensionality in determining ion conductivity. Substitution of Ti for Zr in the A(2)Zr(2-) (y)Ti(y)O(7) (A = Y, Dy, and Gd) series, directly related to yttria stabilized zirconia (a common fuel cell electrolyte), allows controlling ion mobility over wide ranges. In the second scenario we describe the strong enhancement of the conductivity occurring at the interfaces of superlattices made by alternating strontium titanate and yttria stabilized zirconia ultrathin films. We conclude that cooperative effects in oxygen dynamics play a primary role in determining ion mobility of bulk and artificially nanolayered materials and should be considered in the design of new electrolytes with enhanced conductivity.

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This contribution presents the synthesis and thermophysical characterization of seven lanthanide hafnates Ln2Hf2O7 (Ln=Sm3+, Eu3+, Gd3+, Dy3+, Y3+, Ho3+, Yb3+); the title samples were prepared at room temperature by mechanically milling stoichiometric mixtures of the corresponding elemental oxides. Irrespective of the lanthanide ion involved, milling promotes the formation of highly disordered fluoritelike materials. Postmilling thermal treatments facilitate the formation of the fluorite ordered derivative, the pyrochlore structure, but only for the larger lanthanides (Sm3+, Eu3+, Gd3+). Impedance spectroscopy measurements revealed that these materials show a moderate‐to‐good oxygen ion conductivity at high temperatures; furthermore, those adopting the pyrochlore structure give higher σdc and lower Edc than their fluorite analogues (σdc at 750°C>10−3 S·cm−1 vs <5·10−4 S·cm−1, respectively). The same trend also holds for the thermal resistivity at high temperatures; the highest thermal resistivity and thus, lowest κ was obtained for Eu2Hf2O7 (κ~1.3·W·m−1·K−1 at 800°C). Therefore, Ln2Hf2O7 phases might be attractive component materials for electrochemical devices and thermal insulating coatings.