Author: Patricia Álvarez

X.Obradors and T. Puig Molina Supercond. Science & Technology 27, 044003 (2014) DOI:10.1088/0953-2048/27/4/044003 This manuscript reports on the recent progress and the remaining materials challenges in the development of coated conductors (CCs) for power applications and magnets, with a particular emphasis on the different initiatives being active at present in Europe. We first summarize the scientific and technological scope where CCs have been raised as a complex technology product and then we show that there exists still much room for performance improvement. The objectives and CC architectures being explored in the scope of the European project EUROTAPES are widely described and their potential in generating novel breakthroughs emphasized. The overall goal of this project is to create synergy among academic and industrial partners to go well beyond the state of the art in several scientific issues related to CCs’ enhanced performances and to develop nanoengineered CCs with reduced costs, using high throughput manufacturing processes which incorporate quality control tools and so lead to higher yields. Three general application targets are considered which will require different conductor architectures and performances and so the strategy is to combine vacuum and chemical solution deposition approaches to achieve the targeted goals. A few examples of such approaches are described related to defining new conductor architectures and shapes, as well as vortex pinning enhancement through novel paths towards nanostructure generation. Particular emphasis is made on solution chemistry approaches. We also describe the efforts being made in transforming the CCs into assembled conductors and cables which achieve appealing mechanical and electromagnetic performances for power systems. Finally, we briefly mention some outstanding superconducting power application projects being active at present, in Europe and worldwide, to exemplify the strong advances in reaching the demands to integrate them in a new electrical engineering paradigm.

E. Solano, C. Frontera, I. Puente Orench, T. Puig, X. Obradors, S. Ricart and J. Ros Journal of Applied Crystallography 47, 1478 (2014) DOI: 10.1107/S1600576714017452 Neutron and X-ray powder diffraction have been used to investigate the differences between the crystal growth of ferrite magnetic nanoparticles (MFe₂O₄ with M = Mn, Fe, Co, Ni, Zn) by two methodologies: microwave radiation and thermal decomposition routes. Rietveld refinement has been used to extract the cationic distribution, the microstructure and magnetic information. Results for the nanoparticles produced by the two procedures evidence similar cationic distribution, microstructure and magnetic properties: complete cationic disorder for M = Mn and Co, crystal size around/below 10 nm etc. It is thus proven that microwave-assisted growth is a promising eco-friendly synthetic technique for the generation of high-quality nanocrystals with comparable structure and properties to those produced by the thermal methodology, even though the microwave route needs a shorter time and lower annealing temperature to obtain the final crystal nanoparticles.

E. Bartolome, R. Vlad, A. Calleja, M. Aklalouch, R. Guzman, J Arbiol, X. Granados, A. Palau, X. Obradors, T. Puig and A. Usokin Superconductor Science and Technology 26, 125004 (2013) DOI:10.1088/0953-2048/26/12/125004 The superconductor industry is demanding new methodologies to manufacture km-long, high quality coated conductors at high growth rates, using cost-effective, scalable processes. We report on the fabrication by an all-chemical deposition method of highly textured, thick (0.9 μm) inkjet-printed YBCO films, using a Ce_0.9Zr_0.1O₂ (CZO) capping layer deposited by MOD, on top of robust, buffered ^ABADYSZ/SS substrates. Thinner, 0.25 μm spin-coated YBCO films were also analyzed for comparison. The structural study performed by x-ray diffraction, optical, AFM, SEM and TEM microscopy demonstrates the success of the capping layer for enhancing the planarity of the as-received tape and obtaining highly homogeneous and well-textured YBCO films. DC magnetometry granularity analysis was used to determine the mean superconducting grain diameter, ~2.5 μm, and the intra- and intergranular critical current densities of the coated conductors (CCs). For the thin, spin-coated sample, high self-field intragrain critical currents were measured (, 3.3 MA cm⁻² at 5, 77 K). For the thick, inkjet-printed tape was reduced by ~30%, but, notably, the percolative critical current, , was only ~10% smaller at 5 K, thanks to good preservation of the texture. At 77 K, was achieved, implying a critical current of I_c = 117 A/cm-width. AC susceptibility measurements allowed us to demonstrate the high homogeneity of the fabricated CCs, and investigate the magnetic vortex-pinning phase diagram. Remarkably, the thick, inkjet-printed sample showed comparable irreversibility line (IL) and activation energy for thermal depinning, U_e(H), to the thin sample. The present results open new perspectives for the fabrication of high quality-to-cost ratio, all-chemical CCs with yet higher I_c values by inkjet printing multideposition of thicker YBCO layers.

D. Sanchez-Rodriguez, J. Farjas, P Roura, S. Ricart, N. Mestres Andreu, X. Obradors and T. Puig Journal of Physical Chemistry C 117, 20133-20138 (2013) DOI: 10.1021/jp4049742 The possibility of synthesizing functional oxide thin films at low temperature via combustion synthesis is analyzed both experimentally and numerically. To this aim, the decomposition of several oxide precursors [copper and cerium acetates, yttrium trifluoroacetate, and In₂O₃ and La_0.7Sr_0.3MnO₃ (LSMO) nitrate based precursors] has been analyzed by thermal analysis techniques. It is shown that, although these precursors decompose via combustion when they are in the form of powders, their corresponding films show no evidence of combustion. The reason for this different behavior is clearly revealed with numerical simulations. Thin films will hardly experience combustion because the precursor front extinguishes before reaching the precursor–substrate interface leaving a “cool zone” hundreds of micrometers thick. In contrast, it is argued that thin oxide films can be obtained at temperatures lower than powders because of the enhanced gas transport mechanisms that usually limit the decomposition rate.

J. Zabaleta, S. Valencia, F. Kronast, C. Moreno, Patricia Abellan, J. Gazquez Alabart, H. Sepehri-Amin, F. Sandiumenge Ortiz, T. Puig Molina, N. Mestres Andreu and X. Obradors Berenguer Nanoscale 5, 2990-2998 (2013) DOI: 10.1039/C3NR33346A The chemical composition and the magnetic structure of individual La0.7Sr0.3MnO3 (LSMO) ferromagnetic manganite epitaxial nanostructures less than 200 nm in width are explored using Photoemission Electron Microscopy (PEEM). X-ray absorption spectra (XAS) provide separate information on the surface and the bulk composition of the nanoislands and give evidence of Mn2+ present on the surface of otherwise stoichiometric nanostructures. Ferromagnetic domains less than 70 nm are resolved using X-ray magnetic circular dichroism (XMCD), which allows for the detection of magnetic vortex states in both (001)LSMO square and (111)LSMO triangular manganite nanoislands. The evolution of single nanostructures under an in-plane magnetic field is seen to depend on the specific nanoisland size and geometry. In particular, PEEM XMCD imaging allows detecting opposite chiralities as well as a variety of magnetization behaviors for different nanoislands.

R. Guzman, J. Gazquez, V. Rouco, A. Palau, C. Magen, M. Varela, J. Arbiol, X Obradors and T. Puig Appl. Phys. Lett. 102, 081906 (2013) http://dx.doi.org/10.1063/1.4793749 In this letter we use high resolution scanning transmission electron microscopy to study epitaxial YBa₂ Cu ₃O_7−δ (YBCO) nanocomposite thin films. We find that twin boundaries (TB) in YBCOnanocomposite thin films are disturbed by the presence of secondary phase nanoparticles as well as by intergrowths. Secondary phases promote the nucleation of TBs and, at the same time, result in bending, decreasing and changing the TB’s spacing. On the other hand, the local strain ensuing from the partial dislocation associated to Y248 and Y125 intergrowths break the verticalcoherence of TBs. This interaction results in a complex domain structure where twin boundarycoherence is no longer satisfied and twin spacing is reduced down to a few nanometers precluding vortex channeling at low temperatures.