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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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The synthesis of silicon nanocrystals (Si-NC) has attracted a great deal of interest due to their size-dependent optical properties. The appearance of a strong visible photoluminescence (PL) even at room temperature makes this kind of material very interesting for applications in optoelectronics and photonics. In this work, we report on the possibility to control the optical properties of silicon nanostructures by fine tuning of both preparation and processing parameters. Large amount of Si-based nano-powders were prepared by cw CO2 laser pyrolysis of gasphase precursors followed by annealing at different temperatures, in controlled atmosphere. After the heat treatment, the structural and optical analyses revealed the presence of size-controlled optical properties, characterized by the typical Si-NC red-IR emission with lifetime ranging from a hundred of j.is to some ms. Next step was the nano-powder dispersion by several methodologies and their incorporation into a silica sol-gel matrix. The realization of a glassy material that preserves the powder luminescence opens the way to a wide range of applications. To this purpose we focused our attention on the study of the influence of the sol-gel processing steps on the optical properties of Si-nano-powders. Moreover, a study of 1 .54 micron Er emission sensitizing effect from Si-based nanostructures in sol-gel glasses was performed and is presented here.

The redox properties of dense pellets of Ce0.50Zr0.50O2 have been investigated by temperature programmed reduction (TPR) (1023-1373K) and mild temperature oxidation (873K) cycles, X-ray powder diffraction technique (XRD), RAMAN spectroscopy and electrochemical impedance spectroscopy (EIS) have been used to characterize structural and conductivity modifications. The redox treatments promote both the reducibility at lower temperature and the electrical conductivity of this material. A gradual transition from a tetragonal to a pyrochlore cubic phase with the progress of reduction has been observed, while the nature of the phase after reoxidation depends on the temperature of reduction. The promotion of conductivity is correlated with the partial reordering of cationic lattice, but not specifically with the formation of the κ-phase.

Nanocrystalline powders of Y2-xPrxRu2O7 were prepared by a co-precipitation method, and were tested as electrode on ESB and GDC electrolytes by electrochemical impedance spectroscopy in the 300-750°C temperatures range. The electrode polarization was studied as a function of the amount of praseodymium in the cathode material. Both systems, Y2-xPrxRu2O7/ESB and Y2-xPrxRu2O7/GDC, showed a similar variation of the electrode area specific resistance (ASR). Y1.5Pr0.5Ru2O7 cathode material presented the best performance, with ASR value of 0.19 Ωcm2 on ESB and 4.23 Ωcm2 on GDC at 700°C. Furthermore, the change in ASR with the oxygen partial pressure suggested that the rate limiting step is the surface diffusion of the adsorbed oxygen at the electrode surface to the triple-phase boundary. Thus, the low value of resistivity of the Y1.5Pr0.5Ru2O7 in contact with ESB results from a much lower charge transfer resistance compared to the Y2-xPrxRu2O7/GDC system, and a partial solid diffusion at the interface electrode/electrolyte that increases the effective triple phase boundary length. This suggests that Y2-xPrxRu2O7 is a promising material for cathode application in ESB-based electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs).