S. Piñol

Spanish National Research Council, Madrid, Madrid, Spain

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Publications (165)281.75 Total impact

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    ABSTRACT: Chemical solution techniques have been investigated for the growth of both, oxide buffer layers suitable for coated conductors and YBa2Cu3O7 thin films, on single crystal substrates. Growth conditions have been optimised for CeO2 and BaZrO3 buffer layers, leading to high quality epitaxial films (misorientation spread typically below 1°). YBa2Cu3O7 films (thickness: 250 nm) have been grown from trifluoroacetate precursors. The kinetic hindrances for the formation of single phases have been investigated by means of Raman spectroscopy and fluorine analysis. After optimisation of the deposition and growth conditions very high critical currents have been achieved (Jcab=3.2×106 A/cm2 at 77 K and 2.7×107A/cm2 at 5 K).
    Journal of the European Ceramic Society 08/2013; · 2.36 Impact Factor
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    ABSTRACT: La utilización de electrolitos soportados en el ánodo es una estrategia muy útil para mejorar las propiedades eléctricas de las pilas de combustible de óxido sólido, debido a que permiten disminuir considerablemente el espesor de los electrolitos. Para este trabajo, se han preparado exitosamente pilas de combustible de óxido sólido con electrolitos de ceria dopada con Gd, Ce1-xGdxO2-y (CGO) soportados sobre un ánodo formado por un cermet de Ni/CGO. Dichas pilas se han instalado y caracterizado en un reactor de una sola cámara donde se ha hecho circular una mezcla de propano y aire. Para ello, se han preparado mezclas de polvos de NiO y de ceria dopada con gadolinia, con diferentes composiciones y tamaño de partículas, para obtener los ánodos con porosidades apropiadas y así utilizarlos como soporte del electrolito en las pilas. Los polvos de los electrolitos de CGO se han preparado por la técnica sol-gel y se han depositado por �dip coating� con diferentes espesores (15-30 µm) utilizando una tinta preparada a partir de partículas nanométricas dispersadas en una resina comercial. Los cátodos de La1-xSrxCoO3-S (LSCO) se han preparado también por la técnica sol-gel y se han depositado sobre la capa fina del electrolito. Finalmente, las propiedades eléctricas se han determinado en un reactor de una sola cámara dónde el propano se ha mezclado con aire sintético por encima del límite superior de inflamabilidad. En estas condiciones experimentales se han obtenido altas densidades de potencia estables, controlando las velocidades de flujo total de gas transportador y la presión parcial de propano.
    Boletín de la Sociedad Española de Cerámica y Vidrio, ISSN 0366-3175, Vol. 47, Nº. 6, 2008, pags. 319-326. 12/2011;
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    ABSTRACT: Anode-supported SOFC was fabricated using gadolinia doped ceria (GDC) as the electrolyte (15 μm of thickness), Ni-GDC as the anode and La0.5Sr0.5CoO3-δ-GDC as the cathode. Catalytic activities of the electrodes and elec. properties of the cell were detd., using mixts. of methane + air, under single-chamber conditions. This work assessed with special and wide emphasis the effect of temp., gas compn. and total flow rate on the cell performance. As a result, operational temp. range of the fuel cell was approx. between 700 and 800 °C, which agrees with the results corresponding to the catalytic activities of electrodes. While Ni-GDC anode was enough active towards methane partial oxidn. at cell temps. higher than 700 °C, the LSC-GDC cathode was enough inactive towards partial and total oxidn. of methane at cell temps. lower than 800 °C. Under optimized gas compns. (CH4/O2 ratio (1)) and total flow rate (530 mL min-1), power densities of 145 and 235 mW cm-2 were obtained at 705 and 764 °C, resp.
    Fuel Cells 01/2011; 11(1):108-115. · 1.55 Impact Factor
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 29(50).
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    ABSTRACT: On page 2508, in Figure 6, the bar text for the scale should indicate 5 mm instead of 10 mm. Figure 6 has been cor. [on SciFinder(R)]
    Acta Materialia 01/2010; 59(3):1318. · 3.94 Impact Factor
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    ABSTRACT: The main advantages of single-chamber solid oxide fuel cells (SOFCs) with respect to dual-chamber SOFCs, are to simplify the device design and to operate in mixts. of hydrocarbons (methane, propane etc.) and air, with no sepn. between fuel and oxidant. However, this design requires the use of selective electrodes for the fuel oxidn. and the oxidant redn. Electrolyte-supported SOFCs were fabricated using gadolinia-doped ceria (GDC) as the electrolyte, Ni + GDC as the anode and LSC(La0.5Sr0.5CoO3-δ)-GDC-Ag2O as the cathode. The elec. properties of the cell were detd. in mixts. of methane + air and propane + air. The influence of temp., gas compn. and total flow rate on the fuel cell performance was studied. As a result, the power d. increased with increasing temp., total flow rate and hydrocarbon compn. Under optimized gas compns. and total flow conditions, power densities of 70 and 320 mW/cm2 operating on propane at a temp. of 600° and methane (795°C) were obtained, resp. [on SciFinder(R)]
    Boletin de la Sociedad Espanola de Ceramica y Vidrio 01/2010; 49(1):67-74. · 0.40 Impact Factor
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    ABSTRACT: The Young’s modulus (E), hardness (H) and fracture toughness (KIC) of various compositions of gadolinia doped-ceria (GDC, GdxCe1−xO2−x/2, 0.1 ⩽ x ⩽ 0.2) and yttria-stabilized zirconia (YSZ, Y0.08Zr0.92O1.96) electrolytes were investigated by nanoindentation. All samples were produced by the sol–gel method, formed by uniaxial pressure and sintered at 1400 °C. In order to determine the mechanical properties, a Berkovich diamond tip was employed at applied loads of 5, 10, 30, 100 and 500 mN. The results were interpreted by the Oliver–Pharr method and values of KIC were determined using the method of Palmqvist cracks. The residual imprints were observed by field emission scanning electron microscopy. The results obtained showed that the H, E and KIC of GDC decreased with increasing gadolinia concentration, due to the oxygen vacancies generated by the dopant addition. As a result, the mechanical properties of GDC were significantly lower than those of YSZ electrolyte.
    Acta Materialia. 01/2010;
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    ABSTRACT: The mech. properties of thin film gadolinia doped ceria (Gd0.2Ce0.8O1.9, GDC) electrolyte, for solid oxide fuel cells (SOFCs), with different levels of sintering d. were investigated by the nanoindentation technique. Electrolyte thin film supported on Ni-GDC cermet was made by co-sintering at several temps. between 1350 and 1450 °C. The microstructures of the electrolyte films and the cells performances were studied by scanning electron microscope (SEM) and current-voltage tests, resp. In order to det. the mech. properties, a Berkovich indenter was used at different applied loads (30, 50 and 100 mN). Plastic deformation took place, so Oliver and Pharr equations must be applied to evaluate the hardness and Young's modulus of the electrolyte film. The residual nanoindentations were obsd. by optical microscope (M.O.) and field emission scanning electron microscope (FE-SEM). The present study reveals that the nanoindentation is a non-destructive and ideal technique to determinate the quality and the
    Journal of New Materials for Electrochemical Systems 01/2009; 12(4):187-193. · 0.53 Impact Factor
  • M. Morales, S. Piñol, M. Segarra
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    ABSTRACT: Single-chamber fuel cells with electrodes supported on an electrolyte of gadolinium doped ceria Ce1−xGdxO2−y with x = 0.2 (CGO) 200 μm thickness has been successfully prepared and characterized. The cells were fed directly with a mixture of methane and air. Doped ceria electrolyte supports were prepared from powders obtained by the acetyl-acetonate sol–gel related method. Inks prepared from mixtures of precursor powders of NiO and CGO with different particle sizes and compositions were prepared, analysed and used to obtain optimal porous anodes thick films. Cathodes based on La0.5Sr0.5CoO3 perovskites (LSCO) were also prepared and deposited on the other side of the electrolyte by inks prepared with a mixture of powders of LSCO, CGO and AgO obtained also by sol–gel related techniques. Both electrodes were deposited by dip coating at different thicknesses (20–30 μm) using a commercial resin where the electrode powders were dispersed. Finally, electrical properties were determined in a single-chamber reactor where methane, as fuel, was mixed with synthetic air below the direct combustion limit. Stable density currents were obtained in these experimental conditions. Temperature, composition and flux rate values of the carrier gas were determinants for the optimization of the electrical properties of the fuel cells.
    Journal of Power Sources 01/2009; 194(2):961-966. · 5.26 Impact Factor
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    ABSTRACT: Magnetization measurements on a Pr1.85Ce0.15CuO4-y single crystal (Tc = 19.2 K) have provided evidence of strong field-induced diamagnetic fluctuations near the super-conducting transition; the critical zone represents an important fraction (> 33%) of the reversible diamagnetic regime, at any field above 0.05T. The high-field magnetization displays scaling behaviour and the observed scaling functions are in excellent agreement with the predictions for 2D superconducting systems.
    EPL (Europhysics Letters) 07/2007; 24(7):595. · 2.26 Impact Factor
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    ABSTRACT: The colossal magnetoresistance (CMR) of a series of ferromagnetic L2/3Ca1/3MnO3 perovskites is explored for a wide range of lanthanides (L) having different ionic radii. It is shown that the CMR can be tuned through the appropriate size of the lanthanide. The negative magnetoresistance has been modified in this way by two orders of magnitude, reaching ΔR/R values higher than 3105%. We will show that the temperature (TM) where magnetoresistance is maximum correlates with its intensity (ΔR/R) and we will argue that both effects are simply controlled by the bending of the Mn—O—Mn bond. Above TM, the enhancement of resistivity when decreasing the temperature can be described by a Variable Hopping model in which the relevant localization length l is found to be reduced when increasing the lattice distortion; inversely l enhances when applying a magnetic field, thus explaining the observation of a negative magnetoresistance. The giant modification of the electrical resistance goes in parallel with an unusually high magnetic polarizability. We argue that the coupling of itinerant charge carriers (holes) and their reduced mobility when they polarize the localized moments, thus forming magnetic polarons, lie at the heart of the CMR.
    EPL (Europhysics Letters) 01/2007; 34(5):379. · 2.26 Impact Factor
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    S. Piñol, M. Morales, F. Espiell
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    ABSTRACT: The utilization of anode-supported electrolytes is a useful strategy to increase the electrical properties of the solid oxide fuel cells, because it is possible to decrease considerably the thickness of the electrolytes. We have successfully prepared single-chamber fuel cells of gadolinium doped ceria electrolytes Ce1−xGdxO2−y (CGO) supported on an anode formed by a cermet of NiO/CGO. Mixtures of precursor powders of NiO and gadolinium doped ceria with different particle sizes and compositions were analysed to obtain optimal bulk porous anodes to be used as anode-supported fuel cells. Doped ceria electrolytes were prepared by sol–gel related techniques. Then, ceria-based electrolytes were deposited by dip coating at different thicknesses (15–30 μm) using an ink prepared with nanometric powders of electrolytes dispersed in a liquid polymer. Cathodes of La1−xSrxCoO3 (LSCO) were also prepared by sol–gel related techniques and were deposited on the electrolyte thick films. Finally, electrical properties were determined in a single-chamber reactor where propane, as fuel, was mixed with synthetic air below the direct combustion limit. Stable density currents were obtained in these experimental conditions. Flux rate values of the carrier gas and propane partial pressure were determinants for the optimization of the electrical properties of the fuel cells.
    Journal of Power Sources 01/2007; 169(1):2-8. · 5.26 Impact Factor
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    ABSTRACT: Chemical solution deposition (CSD) has recently emerged as a very competitive technique for obtaining epitaxial films of high quality with controlled nanostructure. In particular, the all-CSD approach is considered to be one of the most promising approaches for cost-effective production of second-generation superconducting wires. The trifluoroacetate (TFA) route is a very versatile route for achieving epitaxial YBa2Cu3O7 (YBCO) layers with high critical currents. In this work, recent advances towards improvement of the performance of several conductor architectures based on the YBCO TFA process will be presented. We show that new improved anhydrous TFA precursors allow a significant shortening of the pyrolysis time (~1.5 h), and we have increased the total film thickness in a single deposition using polymeric additives. On the other hand, further understanding of the YBCO nucleation and growth process has allowed us to obtain a controlled microstructure and high critical currents (Jc≈4–5 MA cm−2 and Ic≈300 A cm−1 width at 77 K). The growth conditions (CSD) and post-processing conditions (sputtering and CSD) for the underlying oxide cap and buffer layers (CeO2, BaZrO3, SrTiO3, La2Zr2O7, (La,Sr)MnO3) and of self-organized nanostructures (CeO2, BaZrO3) deposited by CSD have been investigated to obtain high-quality interfaces in multilayered systems. Different single-crystal or metallic substrates (YSZ-IBAD (yttrium stabilized zirconia-ion beam assisted deposition) and Ni-RABiT (rolling assisted biaxial texturing)) have been investigated and long (≈10 m) CSD biaxially textured buffers (CeO2, La2Zr2O7) have been grown on Ni-RABiT substrates using a reel-to-reel system. High-performance TFA-YBCO-coated conductors have been obtained on vacuum-based buffer layers (Ic≈140 A cm−1 width) and on CSD buffer layers grown on IBAD YSZ-SS (stainless steel) substrates. Finally, we report on recent analysis of the magnetic granularity and vortex pinning properties of TFA-YBCO conductors.
    Superconductor Science and Technology 01/2006; 19(3):S13. · 2.76 Impact Factor
  • S. Piñol, O. Castaño
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    ABSTRACT: We have found two different regimes in the kinetics of the YBCO formation depending on the water partial pressure at a constant temperature and total flow rate of the carrier gas. The first regime at low partial water pressure shows continual kinetics curves until the end of YBCO growth and the reaction is controlled chemically. The second regime at high partial water pressure shows irreproducible steps in the kinetics curves during the thin films YBCO growth. In this work we suggest that there is formation of a boundary layer of water (Nernst layer) when the partial water pressure is higher than 20hPa at 795°C for a total gas flow rate lower than 2.4×10−2ms−1. These irreproducible steps dues probably to a water boundary layer formation can be eliminated by increasing the stirring rate of the carrier gas. The reaction order of YBa2Cu3O7−x formation respect to the water pressure is n=0.5 when the water boundary layer is not formed, but the apparent reaction order respect to the partial water pressure is zero or negative when the gas flow rate of the carrier gas is not big enough for the elimination of this water layer. This work also evidences that there is an intermediate step in the kinetics curves before the formation of YBCO. This step, which starts at low temperature during the heating ramp (∼400°C) is attributed to the partial elimination of F from the BaF2 precursor to form oxyfluoride compounds. So, at low total flow gas rates and low partial water pressures, the reaction is controlled by diffusion mechanism due to the formation of a HF boundary layer (Nernst layer), because the apparent order of YBCO formation is one respect to the stirring rate. Nevertheless, at high flow gas rates and low partial water pressures, the YBCO formation is controlled chemically, then the apparent order respect to the stirring rate is zero and the HF Nernst layer is eliminated. The apparent Ea for the oxyfluoride formation at low temperatures is only ∼18Kj/mol indicating that this intermediate reaction is controlled by diffusion mechanism even at high stirring rate and relatively low partial water pressure. The apparent Ea for the YBCO formation at partial water pressures higher than 20hPa for a total flow rate of 2.4×10−2ms−1 is only ∼32Kj/mol, indicating that the reaction control is mainly diffusive or mixed (diffusive and chemist).
    Physica C Superconductivity 01/2006; 450(1):48-55. · 0.72 Impact Factor
  • Salvador Piñol
    Journal of Fuel Cell Science and Technology - J FUEL CELL SCI TECHNOL. 01/2006; 3(4).
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    ABSTRACT: The acetylacetone precursor method was used to obtain powders of different ceria-based Ce0.8Ln0.2O2−δ (Ln = Y, Gd, Sm, La) compositions, and these powders were used to prepare disks which were sintered at 1150 °C after addition of Co nitrate, or at 1500 °C, without Co. These materials were characterized by impedance spectroscopy to distinguish the bulk and grain boundary behaviours. Arrhenius representations of bulk conductivity data show a gradual slope change, indicating defect interactions on cooling to intermediate and relatively low temperatures. Though data for different doped-ceria samples converge in the high temperature range, significant differences in conductivity and activation energy were found at low temperatures. The grain boundary behaviour shows dependence on the trivalent additive (Y, La, Gd or Sm), and the highest grain boundary conductivity for samples obtained without addition of cobalt nitrate was found for samples with La. However, addition of cobalt nitrate and sintering at relatively low temperature enhances the grain boundary conductivity of the remaining materials. The highest specific grain boundary conductivity was then found for samples containing Sm. Differences in grain boundary behaviour were interpreted based on differences in segregation of the rare earth additives for samples without Co-doping and preferential segregation of Co for Co-doped samples.
    Electrochimica Acta. 01/2006;
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    ABSTRACT: The influence of three processing parameters, temperature, gas flow rate and water pressure, on the YBa2Cu3O7 film growth on LaAlO3 single-crystal substrates from trifluoroacetate precursors has been investigated and the optimal film processing conditions to achieve high critical currents have been determined. We have found that the growth conditions maximizing the critical current density are those where the nucleation of a-axis oriented grains is minimized, as determined by μ-Raman spectroscopy. Under these conditions the normal state resistivity is very near to that of single crystals because a vanishingly small film porosity is achieved. Transmission electron microscopy analysis of films quenched from the growth temperature gives some hints for understanding the mechanism linking the film porosity with the concentration of a-axis grains. A cross-linked influence of different processing parameters, such as temperature and water pressure, or water pressure and gas flow, has been demonstrated. The optimal growth temperatures are 790–830 °C, but at these growth temperatures, the critical current density is still dependent on the gas flow rate and water pressure. The optimal processing ranges are a compromise between two different competing phenomena influencing the quality of the films: inhomogeneous film formation due to HF gas stagnancy at small nominal growth rates (low gas flow rate or water pressure) and perturbed crystallinity at high gas flow rates or water pressures.
    Superconductor Science and Technology 07/2005; 18(8):1141. · 2.76 Impact Factor
  • Oscar Castaño, Salvador Piñol
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    ABSTRACT: We have studied in detail the kinetics aspects of Y Ba2Cu3O7−x (YBCO)thin film growth on LaAlO3(100) single crystals by the sol–gel TFA-MOD method, using an in situ fluoride selective electrode. Kinetics curves show that an intermediate step exists before the YBCO formation. This step, which starts at a lower temperature than YBCO formation, consists in a partial elimination of F from the BaF2 precursor to form an oxyfluoride intermediate compound. The total YBCO formation appears at temperatures as high as 700 °C and the activation energy of the reaction is . We have found that at low flow carrier gas rates, the reaction is controlled by diffusion mechanisms and the apparent order of YBCO formation is n = 1 with respect to the stirring rate, but at higher flow rates the YBCO formation is controlled chemically, then the apparent order is zero. The apparent Ea for the oxyfluoride formation at lower temperatures corresponding to the intermediate step is only and the oxyfluoride rate formation increases with the stirring rate, indicating that this intermediate reaction is controlled by diffusion mechanisms.
    Superconductor Science and Technology 10/2004; 17(12):1415. · 2.76 Impact Factor
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    ABSTRACT: We have prepared pure electrolytes of Ce0.8Gd0.2O1.9 (CGO) and Ce0.8Sm0.2O1.9 (CSO), useful for SOFCs, by a sol–gel-related technique like the acrylamide method. This method consists of preparing a solution from the single oxides followed by gelation. Then, the combustion or decomposition of the organic molecules is initiated, producing nanometric calcined powders of the above-mentioned compounds. Thermal treatments were optimized in order to obtain good electrochemical properties of the electrolytes. We have observed that the synthesis temperature to obtain the pure phase is lower for the sol–gel samples than for the pellets prepared by solid-state reaction, and the final density is higher. The microstructure and composition of the powders were characterized by TEM, SEM, and EDX analysis. The electrical properties of the electrolytes were measured by impedance spectroscopy at different temperatures and oxygen partial pressures.
    Journal of Solid State Electrochemistry 07/2004; 8(9):650-654. · 2.28 Impact Factor
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    ABSTRACT: The achievement of low cost deposition techniques for high critical current YBa2Cu3O7 coated conductors is one of the major objectives to achieve a widespread use of superconductivity in power applications. Chemical solution deposition techniques are appearing as a very promising methodology to achieve epitaxial oxide thin films at a low cost, so an intense effort is being carried out to develop routes for all chemical coated conductor tapes. In this work recent achievements will be presented towards the goal of combining the deposition of different type of buffer layers on metallic substrates based on metal–organic decomposition with the growth of YBa2Cu3O7 layers using the trifluoroacetate route. The influence of processing parameters on the microstructure and superconducting properties will be stressed. High critical currents are demonstrated in 'all chemical' multilayers.
    Superconductor Science and Technology 06/2004; 17(8):1055. · 2.76 Impact Factor

Publication Stats

1k Citations
281.75 Total Impact Points

Institutions

  • 1992–2013
    • Spanish National Research Council
      • Institut de Ciència de Materials de Barcelona
      Madrid, Madrid, Spain
  • 1997–2010
    • University of Barcelona
      • Departament de Ciència dels Materials i Enginyeria Metal·lúrgica
      Barcelona, Catalonia, Spain
  • 1992–2009
    • Materials Science Institute of Barcelona
      Barcino, Catalonia, Spain
  • 1998
    • Instituto de Ciencia de Materiales de Aragón
      Caesaraugusta, Aragon, Spain
  • 1992–1998
    • Autonomous University of Barcelona
      • Institut de Ciència de Materials de Barcelona
      Cerdanyola del Vallès, Catalonia, Spain
  • 1990–1997
    • University of Zaragoza
      • Faculty of Sciences (CIENCIAS)
      Zaragoza, Aragon, Spain
    • The University of Warwick
      • Department of Physics
      Coventry, ENG, United Kingdom