Joaquín Sacanell

Phase diagram of La_{5/8-y}Nd_{y}Ca_{3/8}MnO_3 manganites

We report a detailed study of the electric transport and magnetic properties of the La(5/8-y)Nd(y)Ca(3/8)MnO(3) manganite system. Substitution of La(3+) by smaller Nd(3+) ions reduces the mean ionic radius of the A-site ion. We have studied samples in the entire range between La-rich and Nd-rich compounds (0.1<y<0.625). Results of dc magnetization and resistivity show that doping destabilizes the ferromagnetic (FM) character of the pure La compound and triggers the formation of a phase-separated state at intermediate doping. We have also found evidence of a dynamical behaviour within the phase-separated state. A phase diagram is constructed, summarizing the effect of chemical substitution on the system.

Performance of Ag/La0.6Sr0.4Co1-xFexO3 (x = 0 - 0.8) Nanotube Composite Cathodes for IT-SOFCs

We investigated the performance of Ag/La0.6Sr0.4Co1-xFexO3 (x = 0;0.8) nanotube composite cathodes using samaria-doped ceria as electrolyte. These composites were prepared by mixing a commercial Ag paste and La0.6Sr0.4Co1-xFexO3 (x = 0;0.8) nanotubes synthesized by the pore wetting technique using plastic templates. Electrochemical impedance spectroscopy analyses showed that the incorporation of La0.6Sr0.4Co1-xFexO3 nanotubes significantly enhances the performance of the cathode in comparison to pure Ag due to their high specific surface area.

Magnetic properties of cobalt doped ZrO2 nanoparticles: Evidence of Co segregation

We synthesized pure and Co-doped (6.25 12.5 at.) ZrO

Influence of particle size and agglomeration in solid oxide fuel cell cathodes using manganite nanoparticles

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XAFS study on nanostructured (La;Sr)CoO and (La;Sr)(Co;Fe)O IT-SOFC cathodes

nanopowders in order to study their magnetic properties.We analyzed magnetic behavior as a function of the amount of Co and the oxygenation, which was controlled by low pressure thermal treatments. As prepared pure and Co-doped samples are diamagnetic and paramagnetic respectively. Ferromagnetism can be induced by performing low pressure thermal treatments, which becomes stronger as the dwell time of the thermal treatment is increased. This behavior can be reversed, recovering the initial diamagnetic or paramagnetic behavior, by performing reoxidizing thermal treatments. Also, a cumulative increase can be observed in the saturation of the magnetization with the number of low pressure thermal treatments performed. We believe that this phenomenon indicates that cobalt segregation induced by the thermal treatments is the responsible for the magnetic properties of the ZrO

High-performance solid-oxide fuel cell cathodes based on cobaltite nanotubes

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Nanotubes of rare earth cobalt oxides for cathodes of intermediate-temperature solid oxide fuel cells

Co system.

Synthesis and characterization La0.6Sr0.4CoO3 and La0.6Sr0.4Co0.2Fe0.8O3 nanotubes for cathode of solid-oxide fuel cells

In this work we studied the influence of particle size and agglomeration in the performance of solid oxide fuel cell cathodes made with nanoparticles of La0.8Sr0.2MnO3. We followed two synthesis routes based on the Liquid Mix method. In both procedures we introduced additional reagents in order to separated the manganite particles. We evaluated cathodic performance by Electrochemical Impedance Spectroscopy in symmetrical (CATHODE/ELECTROLYTE/CATHODE) cells. Particle size was tuned by the temperature used for cathode sintering. Our results show that deagglomeration of the particles, serves to improve the cathodes performance. However, the dependence of the performance with the size of the particles is not clear, as different trends were obtained for each synthesis route. As a common feature, the cathodes with the lowest area specific resistance are the ones sintered at the largest temperature. This result indicates that an additional factor related with the quality of the cathode/electrolyte sintering, is superimposed with the influence of particle size, however further work is needed to clarify this issue. The enhancement obtained by deagglomeration suggest that the use of this kind of methods deserved to be considered to develop high performance electrodes for solid oxide fuel cells.

Oxygen Reduction Mechanisms in Nanostructured La0.8Sr0.2MnO3 Cathodes for Solid Oxide Fuel Cells

In the last years, extensive research has been devoted to develop novel materials and structures with high electrochemical performance for intermediate-temperatures solid-oxide fuel cells (IT-SOFCs) electrodes. In recent works, we have investigated the structural and electrochemical properties of nanostructured La0.6Sr0.4CoO3 (LSCO) and La0.6Sr0.4(Co;Fe)O3 (LSCFO) cathodes, finding that they exhibit excellent electrocatalytic properties for the oxygen reduction reaction [1,2]. These materials were prepared by a pore-wetting technique using polycarbonate porous membranes as templates. Two average pore sizes were used: 200 nm and 800 nm. Our scanning electronic microscopy (SEM) study showed that the lower pore size yielded nanorods, while nanotubes were obtained with the bigger pore size. All the samples were calcined at 1000°C in order to produce materials with the desired perovskitetype crystal structure. In this work, we analyze the oxidation states of Co and Fe and the local atomic order of LSCO and LSCFO nanotubes and nanowires for various compositions by X-ray absorption spectroscopies. For this purpose we performed XANES and EXAFS studies on both Co and Fe K edges. These measurements were carried out at the D08B-XAFS2 beamline of the Brazilian Synchrotron Light Laboratory (LNLS). XANES spectroscopy showed that Co and Fe only change slightly their oxidation state upon Fe addition. Surprisingly, XANES results indicated that the content of oxygen vacancies is low, even though it is well-known that these materials are mixed ionic-electronic conductors. EXAFS results were consistent with those expected according to the rhombohedral crystal structure determined in previous X-ray powder diffraction investigations.