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Dive into the research topics where S. Piñol is active.

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Featured researches published by S. Piñol.


Superconductor Science and Technology | 2005

The influence of growth conditions on the microstructure and critical currents of TFA-MOD YBa2Cu3O7 films

T. Puig; J.C. González; A. Pomar; Narcis Mestres; O Castaño; M Coll; Jaume Gazquez; F. Sandiumenge; S. Piñol; X. Obradors

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.


Physica C-superconductivity and Its Applications | 1990

Crystal growth and phase diagrams for the Nd2O3-CeO2-CuO system

S. Piñol; J. Fontcuberta; C. Miravitlles; D. McK. Paul

Abstract The phase diagrams for the binary and ternary Nd 2 O 3 -CuO and (0.85Nd 2 O 3 -0.3CeO 2 )- CuO systems are reported and the eutectic points and the liquid lines are determined. We have also explored the crystal growth from molten solutions of compositions 70% CuO-(30- z )% Nd 2 O 3 - z % CeO 2 for a range of CeO 2 concentrations. We show that the composition of the crystals is not uniform for a given z value but the compositional range appears to be quite narrow ( x =0.17(3)) for z =3.6. This concentration produces also the largest crystals (≈10 X 10 X 0.3 mm 3 ).


Journal of Materials Research | 1997

Precipitate size refinement by CeO 2 and Y 2 BaCuO 5 additions in directionally solidified YBa 2 Cu 3 O 7

N. Vilalta; F. Sandiumenge; S. Piñol; X. Obradors

Directional solidification of YBa 2 Cu 3 O 7 has been carried out through a Bridgman technique, and the influence of Y 2 BaCuO 5 and CeO 2 additives on the size of Y 2 BaCuO 5 precipitates has been investigated. It is demonstrated in this work that the most efficient procedure to reduce the size of the Y 2 BaCuO 5 precipitates is to increase the concentration of nucleation centers present in the peritectic decomposition of YBa 2 Cu 3 O 7− x . A small concentration (0.3−1 wt. %) of CeO 2 has a strong influence on the solidification process and on the size of Y 2 BaCuO 5 precipitates. It is shown that when CeO 2 is added, further refinement of the size of precipitates results from the formation of nanometric Y 2 O 3 particles which further enhance the multinucleation effect. We have also observed that coarsening effects are avoided with CeO 2 additives.


Superconductor Science and Technology | 2003

High quality YBa2Cu3O7 thin films grown by trifluoroacetates metalorganic deposition

O Castaño; Andrea Cavallaro; A. Palau; J.C. González; M.D. Rossell; T. Puig; F. Sandiumenge; Narcis Mestres; S. Piñol; A. Pomar; X. Obradors

Chemical solution growth of epitaxial YBa2Cu3O7 thin films on single crystalline substrates has been investigated using trifluoroacetate precursors. The concentration of the starting solution was selected to achieve a final film thickness of 250 nm. First, it is shown that high quality films can only be achieved if an homogeneous nanocrystalline film is obtained after the spin coating deposition and pyrolysis steps. Secondary phases such as BaCuO2, Y2BaCuO5 and CuO remain after the high temperature growth process, when macrosegregation is detected after these initial processing steps. A local degradation of texture associated with macrosegregation is detected by μ-Raman spectroscopy. The influence of growth temperature on the film quality has been analysed and the reaction times have been optimized at each temperature according to the reaction kinetics. In-situ fluoride analysis and μ-Raman spectroscopy have been used to determine the advancement of the formation reaction. The most apparent microstructural modification of these thin film samples with optimized annealing times has been found to be an enhanced porosity for low processing temperatures. The influence of porosity on the normal state resistivity and the critical currents has been evidenced. Optimized processing parameters lead to samples with very high critical currents (Jabc = 3.2 × 106 A cm−2 at 77 K and 2.7 × 107 A cm−2 at 5 K) which demonstrates the capability of the trifluoroacetate metalorganic deposition method for thin film and coated conductor preparation.


Physica C-superconductivity and Its Applications | 1998

Formation and stability of HgCaO2, a competing phase in the synthesis of Hg1−xRexBa2Ca2Cu3O8+δ superconductor

A. Sin; Alfredo G. Cunha; A Calleja; M.T.D. Orlando; Francisco G. Emmerich; E. Baggio-Saitovich; S. Piñol; J.M. Chimenos; X. Obradors

Abstract Thanks to a novel technique (thermobaric analyser or TBA) for measuring the in-situ pressure in quartz tubes, we have investigated the formation and stability of HgCaO2 and its competition with the Hg,Re-1223 in the superconductor synthesis. The pressure determination has enabled us to obtain thermodynamic values such as ΔHf, ΔSf, from which formation temperatures and stability of the binary oxide were determined. This fact has made possible to minimise the presence of this impurity applying suitable heating and cooling ramps in the thermal treatment leading to the formation of Hg,Re-1223. It has been observed that the faster the heating ramp, the less HgCaO2 phase was formed. However, the cooling ramp only influenced the Hg,Re-1223 stability, being more advantageous to perform slow cooling rates. In summary, the in-situ pressure measurement has permitted to ascertain the way to minimise the HgCaO2 impurity content and hence to improve the quality of the ceramic Hg,Re-1223 superconductor.


IEEE Transactions on Applied Superconductivity | 2003

Influence of porosity on the critical currents of trifluoroacetate-MOD YBa/sub 2/Cu/sub 3/O/sub 7/ films

O Castaño; Andrea Cavallaro; A. Palau; J.C. González; M. Rosell; T. Puig; S. Piñol; Narcis Mestres; F. Sandiumenge; A. Pomar; X. Obradors

The influence of porosity on the superconducting properties have been investigated on YBa/sub 2/Cu/sub 3/O/sub 7/ thin films deposited on LaAlO/sub 3/ [100] substrates by the so-called Trifluoroacetate (TFA) route. Micro-Raman spectroscopy have been used to determine the concentration of c-axis grains /spl delta/ in different samples and their influence on the final film porosity as observed from SEM imaging. This has been compared with measurements of resistivity and critical currents in the same samples. We prove that this /spl delta/ fraction is the main parameter controlling the porosity and hence the normal-state resistivity of the thin films. The optimization of the microstructure of these YBa/sub 2/Cu/sub 3/O/sub 7/ TFA films allow to have high critical currents : J/sub c/ = 3 /spl times/ 10/sup 6/ A/cm/sup 2/ at 77 K.


Superconductor Science and Technology | 1999

Influence of precursor oxygen stoichiometry on the formation of Hg, Re-1223 superconductors

A. Sin; Alfredo G. Cunha; A Calleja; M.T.D. Orlando; Francisco G. Emmerich; Elisa Baggio-Saitovitch; M. Segarra; S. Piñol; X. Obradors

Thanks to a novel technique (thermobaric analyser or TBA) for measuring the in situ pressure in quartz tubes, we have investigated the precursor quality for the synthesis of the superconductor Hg-1223 which is an essential parameter to control. We have made this study on the samples and we can conclude that this superconductor phase requires a ceramic precursor sintered in a low mixture gas flux. An excessively oxygenated precursor leads to overdoped superconducting phases, presence of other members with lower n, and some unreacted precursor. The precursor oxygenation degree also modifies the kinetics of formation of and the partial melting of the superconductor material may be affected.


Applied Physics Letters | 1995

Aging of critical currents and irreversibility line in melt textured YBa2Cu3O7

B. Martínez; F. Sandiumenge; S. Piñol; N. Vilalta; J. Fontcuberta; X. Obradors

The critical currents and the irreversibility line of bulk melt textured YBa2Cu3O7 have been found to evolve with the increase of the oxygenation time. A strong field‐dependent reduction of the critical currents is observed which finally leads to a downward shift of the irreversibility line. Transmission electron microscopy micrographs of aged samples display a huge increase in the concentration of stacking faults near the microcracks and at the YBa2Cu3O7‐Y2BaCuO5 interfaces. Low field ac susceptibility measured with H∥ab shows a strong reduction of the screening capability thus meaning that nonsuperconducting planar defects parallel to the ab planes have been created. We suggest that an enhanced two‐dimensional behavior of the vortex flux lattice occurs when H∥c as a consequence of this layered defective structure.


Journal of Materials Research | 1997

Precipitate size refinement by CeO{sub 2} and Y{sub 2}BaCuO{sub 5} additions in directionally solidified YBa{sub 2}Cu{sub 3}O{sub 7}

N. Vilalta; F. Sandiumenge; S. Piñol; X. Obradors

Directional solidification of YBa 2 Cu 3 O 7 has been carried out through a Bridgman technique, and the influence of Y 2 BaCuO 5 and CeO 2 additives on the size of Y 2 BaCuO 5 precipitates has been investigated. It is demonstrated in this work that the most efficient procedure to reduce the size of the Y 2 BaCuO 5 precipitates is to increase the concentration of nucleation centers present in the peritectic decomposition of YBa 2 Cu 3 O 7− x . A small concentration (0.3−1 wt. %) of CeO 2 has a strong influence on the solidification process and on the size of Y 2 BaCuO 5 precipitates. It is shown that when CeO 2 is added, further refinement of the size of precipitates results from the formation of nanometric Y 2 O 3 particles which further enhance the multinucleation effect. We have also observed that coarsening effects are avoided with CeO 2 additives.


Applied Physics Letters | 1996

Extraordinary thermopower in magnetoresistive (La1−xYx)0.67Ca0.33MnO3 oxides

J. Fontcuberta; A. Seffar; X. Granados; J.L. García-Muñoz; X. Obradors; S. Piñol

We report that the thermopower Q(T) of the (La1−xYx)0.67Ca0.33MnO3 (x=0–0.25) magnetoresistive oxides, displays a pronounced peak at temperatures Ts close to the ferromagnetic ordering temperature. The temperature Ts decreases monotonously when increasing x whereas the maximal Q(Ts) is found to increase with the Y contents. The huge enhancement of Q at Ts is found to be as high as 460% for x=0.25. It is shown that the extraordinary thermopower observed at Ts results from the reduced charge carrier mobility when approaching Ts and the variation of Q(T) with the Y contents reflects the accompanying band narrowing.

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