Staff directory

Anna Magrasó Solà

Postdoctoral Researcher
anna.magraso(ELIMINAR)@icn2.cat
Nanomaterials Growth Division

Publications

2018

  • Optimisation of growth parameters to obtain epitaxial Y-doped BaZrO3 proton conducting thin films

    Magrasó A., Ballesteros B., Rodríguez-Lamas R., Sunding M.F., Santiso J. Solid State Ionics; 314: 9 - 16. 2018. 10.1016/j.ssi.2017.11.002.

    We hereby report developments on the fabrication and characterization of epitaxial thin films of proton conducting Y-doped BaZrO3 (BZY) by pulsed laser deposition (PLD) on different single crystal substrates (MgO, GdScO3, SrTiO3, NdGaO3, LaAlO3 and sapphire) using Ni-free and 1% Ni-containing targets. Pure, high crystal quality epitaxial films of BZY are obtained on MgO and on perovskite-type substrates, despite the large lattice mismatch. The deposition conditions influence the morphology, cell parameters and chemical composition of the film, the oxygen partial pressure during film growth being the most determining. Film characterization was carried out using X-ray diffraction, transmission electron and atomic force microscopies, wavelength dispersive X-ray spectroscopy and angle-resolved X-ray photoelectron spectroscopy. All films show a slight tetragonal distortion that is not directly related to the substrate-induced strain. The proton conductivity of the films depends on deposition conditions and film thickness, and for the optimised conditions its total conductivity is slightly higher than the bulk conductivity of the target material (3 mS/cm at 600 °C, in wet 5% H2/Ar). The conductivities are, however, more than one order of magnitude lower than the highest reported in literature and possible reasoning is elucidated in terms of local and extended defects in the films. © 2017 Elsevier B.V.


2016

  • Comparison of the local and the average crystal structure of proton conducting lanthanum tungstate and the influence of molybdenum substitution

    Magrasó A., Frontera C. Dalton Transactions; 45 (9): 3791 - 3797. 2016. 10.1039/c5dt04659a. IF: 4.177

    We report on the comparison of the local and average structure reported recently for proton conducting lanthanum tungstate, of general formula La28-xW4+xO54+δv2-δ, and the impact of molybdenum-substitution on the crystal structure of the material. Partial replacement of W with 10 and 30 mol% Mo is investigated here, i.e. La27(W1-xMox)5O55.5 for x = 0.1 and 0.3. This study addresses the interpretation and the description of a disordered cation and anion sublattice in this material, which enables the understanding of the fundamental properties related to hydration, transport properties and degradation in lanthanum tungstate. The report shows that Mo-substituted lanthanum tungstate is a promising material as a dense oxide membrane for hydrogen separation at intermediate temperatures. © The Royal Society of Chemistry 2016.


  • Effect of tri- and tetravalent metal doping on the electrochemical properties of lanthanum tungstate proton conductors

    Porras-Vázquez J.M., Dos Santos-Gómez L., Marrero-López D., Slater P.R., Masó N., Magrasó A., Losilla E.R. Dalton Transactions; 45 (7): 3130 - 3138. 2016. 10.1039/c5dt03833b. IF: 4.177

    Rare-earth tungstates (La28-yW4+yO54+δ□2-δ) have attracted attention recently because of their relatively high proton-electron conductivity and high stability in a CO2 environment. Since doping on the tungsten-site may increase the conductivity, a new series of compounds with composition La5.5W1-xMxO11.25-δ (M = Al, Ti and Zr; x = 0, 0.05 and 0.10) have been investigated. The crystal structure of these materials has been studied using X-ray and time-of-flight neutron powder diffraction by Rietveld analysis. The concentration of oxygen vacancies for hydration in the structure has been indirectly determined by thermogravimetric analysis, and the total conductivity in several pO2, pH2O and pD2O atmospheres has been studied by impedance spectroscopy. An increase in the conductivity is observed, ranging from 4.1 mS cm-1 for the undoped sample to 9.2 mS cm-1 for La5.5W0.9Ti0.1O11.25-δ, in wet N2 at 800°C. © The Royal Society of Chemistry 2016.


  • The Band Gap of BaPrO3 Studied by Optical and Electrical Methods

    Schrade M., Magrasó A., Galeckas A., Finstad T.G., Norby T. Journal of the American Ceramic Society; 99 (2): 492 - 498. 2016. 10.1111/jace.13961. IF: 2.787

    We report on measurements of the electrical and optical properties of BaPrO3. The temperature dependences of the electrical conductivity σ and the Seebeck coefficient α of polycrystalline samples were studied over a wide temperature range (300°C-1050°C). At lower temperatures, the observed charge transport can be described as thermally activated hopping of electron-based small polarons with an activation energy of 0.37 eV. An observed change in temperature dependence of both σ and α around 700°C was observed and interpreted as a transition from extrinsic to intrinsic carrier transport. The intrinsic conduction can be modeled with an apparent electrical band gap of ~2 eV. Optical absorption and emission spectroscopy in the UV-VIS-NIR range revealed a series of characteristic absorption thresholds and the type of optical transitions was identified by combining transmittance and diffuse-reflectance spectroscopy methods. An absorption edge of indirect type with onset at 0.6 eV is attributed to small polaron effects. The higher lying absorption thresholds of direct origin positioned at around 1.8 and 3.8 eV are correlated with thermal activation parameters from electrical measurements and discussed in terms of the band gap of BaPrO3. © 2015 The American Ceramic Society.


2015

  • On the development of proton ceramic fuel cells based on Ca-doped LaNbO4 as electrolyte

    Norby T., Magrasó A. Journal of Power Sources; 282: 28 - 33. 2015. 10.1016/j.jpowsour.2015.02.027. IF: 6.217

    We review the key properties of Ca-doped LaNbO4 (LCNO) and related materials for use as proton conducting electrolyte, from the discovery of its proton conductivity, through developments of synthesis and production, anodes and cathodes, to demonstrations of it in laboratory fuel cells, exemplified through published and new results from a range of collaborative projects in Norway and Europe the last years. Important new knowledge has been obtained concerning the reliable synthesis of line compounds like LaNbO4, B-site doping and co-doping, grain boundary resistance, phase transformations, thin film fabrication, and electrodes for proton conducting ceramics. However, as LCNO still requires films too thin for reliable fabrication of large areas and operation over prolonged times, and since cathodes with acceptable electrocatalytic performance have not been identified, one must conclude that high-power fuel cells (and steam electrolysers) based on LCNO are not viable. © 2015 Published by Elsevier B.V.


  • Reduced long term electrical resistance in Ce/Co-coated ferritic stainless steel for solid oxide fuel cell metallic interconnects

    Magraso A., Falk-Windisch H., Froitzheim J., Svensson J.-E., Haugsrud R. International Journal of Hydrogen Energy; 40 (27): 8579 - 8585. 2015. 10.1016/j.ijhydene.2015.04.147. IF: 3.313

    The present study is focused on the influence of selected coatings on a ferritic stainless steel (Sanergy HT™, Sandvik) on the evolution of the area specific resistance (ASR) as a function of time at high temperature. The samples are exposed in humidified air at 850 °C for up to 4200 h. It combines long-term ASR measurements with the thermogravimetric behavior and microstructural analysis of the cross sections by scanning electron microscopy. The results show that uncoated and Co-coated Sanergy HT™ exhibit similar oxidation kinetics and comparable ASRs, while a combined Ce/Co coating improves oxidation resistance and, consequently, reduces the ASR significantly. Other reports have earlier shown that Co- (and Ce/Co)-coated Sanergy HT™ reduces the evaporation of volatile chromium species. Overall, the study indicates that Ce/Co-coatings will render substantially improved performance for ferritic steel interconnects for solid oxide fuel cells. Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.