Caractérisations physico-chimiques et électriques de films ferroélectriques synthétisés par voie hydrothermale

National audienc

Leaf architecture and ecophysiology of an early basal eudicot from the Early Cretaceous of Spain

Iterophyllum lobatum gen. et sp. nov. is reported from the late Barremian lithographic limestones of Las Hoyas, Spain. It consists of a simple, petiolate leaf, with a pinnately lobed lamina. The dentate thickened margin bears chloranthoid-like glands at lobe apices and sinuses. The venation is pinnate and craspedodromous, with three discernible vein orders. Based on the low regularity of vein course and angles and the low leaf rank, such a venation pattern may represent an early evolved leaf archetype in early basal eudicots. An acropetal leaf development mode in I. lobatum is similar to that in several living Papaveraceae. The leaf architecture and ecophysiology, particularly the vein widths and the glands, indicate that I. lobatum leaves were aerial. The plant grew close to water in the wetland terrestrial ecosystem of Las Hoyas. Iterophyllum lobatum might have been an opportunist species in early ecological succession stages after wildfires

Ca 3 Co 4 O 9−δ : A Thermoelectric Material for SOFC Cathode

International audienc

Ru-Pyrochlores: Compositional Tuning for Electrochemical Stability as Cathode Materials for IT-SOFCs

International audienceUsing XRD, impedance spectroscopy, and XPS, it was shown that both Bi2Ru2O7 and Pb2Ru2O6.5, generally announced as attractive electrode materials for IT-SOFCs, chemically react with CGO. In addition, a never-mentioned time-instability under electrochemical measurements with YZS as electrolyte mediates the polarization tests. For Pb2Ru2O6.5, long time experiments (stabilization time > 900 h, previously to complementary electrochemical tests), yields strong increasing of the resistance polarization. Concerning Bi2Ru2O7, a partial transformation into Bi3Ru3O11 is observed after impedance measurements. The investigation of the Bi2−xMxRu2O7−δ (M = Sr, Pb) solid solutions was performed with the aim to improve the catalytic/electric properties. For low x values, it shows a time and chemical stabilization of the electrode/electrolyte cells, able to preserve high electrode performances of these materials. For higher substitution, the chemical/electrochemical instability reappears. According to our polarization measurements versus oxygen pressure and temperature in the so-called “stabilized” samples, the electrode performance appears limited by the diffusion of adsorbed oxygen on the triple point boundary. It is fully compatible with the metallic behavior checked in all the series

Characterization of oxygen transport in lanthanum chromo-manganites by 18O/16O isotope exchange

International audienc

Electrostatic spray deposition of Ca3Co4O9 + δ layers to be used as cathode materials for IT-SOFC

International audienceIn this paper, the deposition of Ca3Co4O9 + δ layers on CGO substrates using electrostatic spray deposition (ESD) technique, starting from calcium and cobalt nitrates as precursor salts, is reported. The microstructure was investigated as a function of process parameters such as nozzle-to-substrate distance, solvent composition, substrate temperature, flow rate and deposition time, based on an upper and a lower value. Films with controlled microstructures were obtained after annealing at 880 °C for 2 h in air. The formation of Ca3Co4O9 + δ was confirmed by X-ray diffraction, which also showed evidence of Co3O4 traces. As shown by in-situ X-ray diffraction, Ca3Co4O9 + δ starts to form at 625 °C and decomposes at 950 °C, but the transformation is reversible. Interestingly, the initial morphology of the films was maintained after annealing at either 700 or 880 °C, with the appearance of faceted crystals forming a gypsum flower-like microstructure. AC impedance spectroscopy was carried out at intermediate temperatures (600–800 °C) under air on 2 batches of symmetrical cells based on ESD and screen-printed electrodes, respectively. This work confirmed the beneficial impact of the ESD technique. The area-specific resistance was improved by at least 23% at 600 °C and 40% at 800 °C for the sample prepared by ESD compared to the reference one prepared by screen printing. This improvement was explained by a better interface between the electrode and the electrolyte

«Transport properties in promising cobaltites as SOFC cathode»

International audienceno abstrac

Original positively charged nanoflakes by liquid exfoliation of layered oxybromide cobaltites

International audienceFor the synthesis of novel positively charged 2D-elementary blocks, we have focused on the exfoliation of recent mixed valent Co3+/4+ oxy-bromides, namely the 14H-Ba7Co6BrO17 and 18R-Ba6Co5BrO14 phases built on hexagonal-perovskite blocks separated by [Ba2O2Br](-)spacers. Here, we show that the exfoliation in butanol leads to positive nanoblocks in colloidal suspensions, as confirmed Zetametry measurements. Full structural characterization was performed by TEM, EDS, Raman and IR spectroscopies, AFM, X-ray absorption spectroscopy (XANES and DANES) and synchrotron X-ray diffraction (in-plane and out of plane). Combination of all these techniques results into a detailed description of crystalline flat particles (similar to 100 nm large and similar to 10 nm thick) where the Co3+/4+ mixed oxidation state, as well as the local Co environment, are preserved after the exfoliation process. In-plane and out of plane synchrotron X-ray diffraction confirms a strong preferred deposition (001) planes. The original bulk materials showing intrinsic ferromagnetism in the elementary blocks, the magnetic properties of the delaminated nanoparticles are also presented here. Finally, we have prepared new positive nanometric bricks based on hexagonal perovskite structure, rare objects in condensed matter

Original positively charged nanoflakes by liquid exfoliation of layered oxybromide cobaltites

For the synthesis of novel positively charged 2D-elementary blocks, we have focused on the exfoliation of recent mixed valent Co3+/4+ oxy-bromides, namely the 14H-Ba7Co6BrO17 and 18R-Ba6Co5BrO14 phases built on hexagonal-perovskite blocks separated by [Ba2O2Br](-)spacers. Here, we show that the exfoliation in butanol leads to positive nanoblocks in colloidal suspensions, as confirmed Zetametry measurements. Full structural characterization was performed by TEM, EDS, Raman and IR spectroscopies, AFM, X-ray absorption spectroscopy (XANES and DANES) and synchrotron X-ray diffraction (in-plane and out of plane). Combination of all these techniques results into a detailed description of crystalline flat particles (similar to 100 nm large and similar to 10 nm thick) where the Co3+/4+ mixed oxidation state, as well as the local Co environment, are preserved after the exfoliation process. In-plane and out of plane synchrotron X-ray diffraction confirms a strong preferred deposition (001) planes. The original bulk materials showing intrinsic ferromagnetism in the elementary blocks, the magnetic properties of the delaminated nanoparticles are also presented here. Finally, we have prepared new positive nanometric bricks based on hexagonal perovskite structure, rare objects in condensed matter

«Oxygen transport and electrochemical performances in Ca₃Co₄O₉ derivatives as SOFC cathode»

International audienc