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Y 2Àx Pr x Ru 2 O 7 (0rxr2) pyrochlore powders were prepared using a precipitation method, which allowed control of their composition and morphology. Materials structure and morphology were characterized by X-ray diffraction analysis and field emission scanning electron microscopy, respectively. All the synthesized powders exhibited a single pyrochlore phase with particle size depending on the Pr content. Powders with Pr content smaller than 25 mol% were nanometric. X-ray photoelectron spectroscopy analysis revealed a mixed oxidation state of both Pr and Ru, and a variation of the oxidation state of the elements in response to oxygen partial pressure changes. Electrical conductivity measurements were performed by dc 4-probe method at several temperatures, showing that increasing the Pr content in the A site of the pyrochlore structure increased the oxide electrical conductivity.

The effect of redox cycles on the reducibility, structural, and electrical properties of dense pellets of ceria-zirconia solid solutions has been investigated by temperature programmed reduction studies, X-ray diffraction technique, Raman spectroscopy, and electrochemical impedance spectroscopy. Similarities and differences among the compositions with high ͑Ce 0.80 Zr 0.20 O 2 ͒, intermediate ͑Ce 0.50 Zr 0.50 O 2 ͒, and low ͑Ce 0.20 Zr 0.80 O 2 ͒ amounts of ceria were evaluated in view of their application as active components for solid oxide fuel cell ͑SOFC͒ anodes. Cycles of reduction and reoxidation, respectively, at 1273 and 873 K, promote the reduction of all the compositions investigated, shifting it at a lower temperature. Moreover, redox treatments cause a significant change in the crystal structure of Ce 0.50 Zr 0.50 O 2 , ultimately leading to the formation of cubic pyrochlore phases as the reduction temperature increases. The correlations among structural changes, redox, and electrical properties of these materials are discussed.

Nanocrystalline powders of Y2Ru2O7 and Y2-xPrxRu2O7 were prepared by a co-precipitation method. Pr was chosen as the A- site dopant in order to increase the electrical conductivity of Y2Ru2O7. Phase and morphology were studied by XRD and FE- SEM, which showed both systems exhibit a particle size of about 100 nm, and the doped powders were single pyrochlore phase. The electrical conductivity of a dense bar of Y2- xPrxRu2O7 was measured at several temperatures by d.c. 4-probe method, while the electrochemical properties of Y2-xPrxRu2O7 pyrochlores were tested in contact to ESB electrolytes, using Electrochemical Impedance Spectroscopy (EIS) in air. The Y2- xPrxRu2O7 on ESB electrolyte solid-state cells presents a significant decrease of electrodes impedance.

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