Epitaxial YBa2Cu3O7-x nanocomposite thin films from colloidal solutions

A methodology of general validity to prepare epitaxial nanocomposite films based on the use of colloidal solutions containing different crystalline preformed oxide nanoparticles (ex situ nanocomposites) is reported. The trifluoroacetate (TFA) metal-organic chemical solution deposition route is used with alcoholic solvents to grow epitaxial YBaCuO (YBCO) films. For this reason stabilizing oxide nanoparticles in polar solvents is a challenging goal. We have used scalable nanoparticle synthetic methodologies such as thermal and microwave-assisted solvothermal techniques to prepare CeO and ZrO nanoparticles. We show that stable and homogeneous colloidal solutions with these nanoparticles can be reached using benzyl alcohol, triethyleneglycol, nonanoic acid, trifluoroacetic acid or decanoic acid as protecting ligands, thereby allowing subsequent mixing with alcoholic TFA solutions. An elaborate YBCO film growth analysis of these nanocomposites allows the identification of the different relevant growth phenomena, e.g. nanoparticles pushing towards the film surface, nanoparticle reactivity, coarsening and nanoparticle accumulation at the substrate interface. Upon mitigation of these effects, YBCO nanocomposite films with high self-field critical currents (J ∼ 3-4 MA cm at 77 K) were reached, indicating no current limitation effects associated with epitaxy perturbation, while smoothed magnetic field dependences of the critical currents at high magnetic fields and decreased effective anisotropic pinning behavior confirm the effectiveness of the novel developed approach to enhance vortex pinning. In conclusion, a novel low cost solution-derived route to high current nanocomposite superconducting films and coated conductors has been developed with very promising features.All authors acknowledge the EU (EU-FP7 NMP-LA-2012-280432 EUROTAPES project). ICMAB acknowledges MINECO (MAT2014-51778-C2-1-R) and Generalitat de Catalunya (2014SGR 753 and Xarmae). UGhent acknowledges the Special Research Fund (BOF), the Research Foundation Flanders (FWO) and the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT). TEM microscopy work was conducted in the Catalan Institute of Nanoscience and Nanotechnology (ICN2). The authors acknowledge the ICN2 Electron Microscopy Division for offering access to their instruments and expertise. Part of the STEM microscopy work was conducted in 'Laboratorio de Microscopias Avanzadas' at the Instituto de Nanociencia de Aragon—Universidad de Zaragoza. The authors acknowledge the LMA-INA for offering access to their instruments and expertise. JG and MC also acknowledge the Ramon y Cajal program (RYC-2012-11709 and RYC-2013-12448 respectively).Peer Reviewe

High Performance of Superconducting YBa2Cu3O7 Thick Films Prepared by Single-Deposition Inkjet Printing

Inkjet printing (IJP) is a very appealing cost-effective deposition technique to achieve large-area solution-derived functional films. For many applications, it is very challenging to increase the film thickness in order to achieve competitive performance, for instance, high critical currents in superconducting films. In this paper, the preparation of superconducting YBa2Cu3O7 thick films (∼1.1 μm) using a single deposition is reported. Specific rules for ink design, deposition protocols, and pyrolysis processes are provided. The most important aspect is to formulate an ink with a solvent having a high boiling point that keeps the whole film wet during deposition to avoid liquid movement due to coffee-ring effects. An additional success has been to modify the ink with a photocurable polyacrylic ester varnish which after polymerization with a UV LED lamp helps keep homogeneous thickness. This varnish also helped avoid the generation of film instabilities (wrinkling or cracking) during pyrolysis. Homogeneous pyrolyzed thick films are transformed into epitaxial thick films with high critical currents. The IJP process is shown to be valid to prepare nanocomposite films using colloidal inks including pre-prepared BaZrO3 nanoparticles. The nanocomposite thick films display enhanced vortex pinning, thus keeping high critical currents under high magnetic fields.The authors acknowledge the EUROTAPES project (EU-FP7 NMP-LA-2012-280432), COACHSUPENERGY (MAT2014- 51778-C2-1-R and MAT2014-51778-C2-2-R), SUMATE (RTI2018-095853-BC21 and RTI2018-095853-B-C22) cofinanced by the European Regional Development Fund and SUPERINKS (RTC-2015-3840-S) from MINECO (cofinanced by the European Regional Development Fund), 2017-SGR 753 from Generalitat de Catalunya, and COST Action NANOCOHYBRI (CA16218). ICMAB authors acknowledge the Center of Excellence awards Severo Ochoa SEV2015-0496 and CEX2019-000917-S. The authors acknowledge the Scientific Services at ICMAB, ICN2 Electron Microscopy Division, and LMA-INA from Aragon. They also acknowledge KAO Chimigraf for providing varnishes and Bruker HTS for providing metallic substrates.Peer reviewe

Acetylsalicylic acid prevents intermittent hypoxia-induced vascular remodeling in a murine model of sleep apnea

Study objectives: Chronic intermittent hypoxia (CIH), a hallmark feature of obstructive sleep apnea (OSA), induces accelerated atherogenesis as well as aorta vascular remodeling. Although the cyclooxygenase (COX) pathway has been proposed to contribute to the cardiovascular consequences of OSA, the potential benefits of a widely employed COX-inhibitor such (acetylsalicylic acid, ASA) on CIH-induced vascular pathology are unknown. Therefore, we hypothesized that a common non-selective COX inhibitor such as ASA would attenuate the aortic remodeling induced by CIH in mice.Methods: 40 wild-type C57/BL6 male mice were randomly allocated to CIH or normoxic exposures (N) and treated with daily doses of ASA or placebo for 6 weeks. At the end of the experiments, intima-media thickness (IMT), elastin disorganization (ED), elastin fragmentation (EF), length between fragmented fiber endpoints (LFF), aortic wall collagen abundance (AC) and mucoid deposition (MD) were assessed.Results: Compared to N, CIH promoted significant increases in IMT (52.58 +/- 2.82 mu m vs. 46.07 +/- 4.18 m, p < 0.003), ED (25.29 +/- 14.60% vs. 4.74 +/- 5.37%, p < 0.001), EF (5.80 +/- 2.04 vs. 3.06 +/- 0.58, p < 0.001), LFF (0.65 +/- 0.34% vs. 0.14 +/- 0.09%, p < 0.001), AC (3.43 +/- 1.52% vs. 1.67 +/- 0.67%, p < 0.001) and MD (3.40 +/- 2.73 mu m(2) vs. 1.09 +/- 0.72 mu m(2), p < 0.006). ASA treatment mitigated the CIH-induced alterations in IMT: 44.07 +/- 2.73 mu m; ED: 10.57 +/- 12.89%; EF: 4.63 +/- 0.88; LFF: 0.25 +/- 0.17% and AC: 0.90 +/- 0.13% (p < 0.05 for all comparisons).Conclusions: ASA prevents the CIH-induced aortic vascular remodeling, and should therefore be prospectively evaluated as adjuvant treatment in patients with OSA

Superconducting YBa 2 Cu 3 O 7–δ Nanocomposites Using Preformed ZrO 2 Nanocrystals: Growth Mechanisms and Vortex Pinning Properties

Keukeleere, Katrien De et al.Although high temperature superconductors are promising for power applications, the production of low-cost coated conductors with high current densities—at high magnetic fi elds—remains challenging. A superior superconducting YBa 2 Cu 3 O 7–δ nanocomposite is fabricated via chemical solution deposition (CSD) using preformed nanocrystals (NCs). Preformed, colloidally stable ZrO 2 NCs are added to the trifl uoroacetic acid based precursor solution and the NCs’ stability is confi rmed up to 50 mol% for at least 2.5 months. These NCs tend to disrupt the epitaxial growth of YBa 2 Cu 3 O 7–δ , unless a thin seed layer is applied. A 10 mol% ZrO 2 NC addition proved to be optimal, yielding a critical current density J C of 5 MA cm −2 at 77 K in self-fi eld. Importantly, this new approach results in a smaller magnetic fi eld decay of J C (H//c) for the nanocomposite compared to a pristine fi lm. Furthermore, microstructural analysis of the YBa 2 Cu 3 O 7–δ nanocomposite fi lms reveals that different strain generation mechanisms may occur compared to the spontaneous segregation approach. Yet, the generated nanostrain in the YBa 2 Cu 3 O 7–δ nanocomposite results in an improvement of the superconducting properties similar to the spontaneous segregation approach. This new approach, using preformed NCs in CSD coatings, can be of great potential for high magnetic fi eld applications.K.D.K. and P.C. contributed equally to this work. This work was fi nancially supported by a BOF research fund of Ghent University ( BOF11/ DOC/286 ), FWO Flanders ( F08512 ), and Eurotapes, a collaborative project funded by the European Community’s Seven Framework Program ( EU-FP7 NMP-LA-2012-280432 ). The authors also acknowledge MINECO and FEDER funds for MAT2014-51778-C2-1-R and the Center of Excellence award Severo Ochoa SEV-2015-0496 , and SGR753 from the Generalitat of Catalunya. M.C. acknowledges RyC Contract 2013–12448.Peer reviewe

Epitaxial superconducting GdBa2Cu3O7−δ/Gd2O3 nanocomposite thin films from advanced low-fluorine solutions

Cayado, Pablo et al.We have employed the CSD method to synthesize GdBCO and GdBCO–Gd2O3 nanocomposite 250–300 nm thin films. For this we have designed a new low-fluorine solution never used before in the synthesis of GdBCO thin films that allows us to reduce the HF release by 80% and increase the reproducibility of the pyrolysis process. The growth of these thin films required a new thermal process to be designed, which we refer to as 'flash-heating', where the heating rate is extremely fast (~600 °C min−1). The structure and the superconducting properties of the pristine GdBCO films are excellent, showing a (00 l) epitaxial orientation of the GdBCO grains and T c values that reach 92.8 K, which means an enhancement of more than 1 K with respect to standard YBCO films. The calculated J c inside the grains (${J}_{{\rm{c}}}^{{\rm{G}}}$) also presents remarkable values: ${J}_{{\rm{c}}}^{{\rm{G}}}$(5 K) ~ 40 MA cm−2 and ${J}_{{\rm{c}}}^{{\rm{G}}}$(77 K) ~ 3.3 MA cm−2. Finally, the GdBCO–Gd2O3 nanocomposites films, with a 20% mol of Gd2O3, exhibit superior superconducting properties and pinning performances with respect to GdBCO pristine films.This work was financially supported by Eurotapes, a collaborative project funded by the European Community's Seven Framework Program (EU-FP7 NMP-LA-2012-280432). We also acknowledge MINECO and FEDER funds for the COACHSUPENERGY project (MAT2014-51778-C2-1-R) and the Center of Excellence award Severo Ochoa SEV-2015-0496, and SGR753 from the Generalitat of Catalunya. B M acknowledges an FI fellowship from MINECO. M C and J G acknowledge the Ramon y Cajal programs (RYC-2013-12448 and RYC-2012-11709, respectively)Peer reviewe

Control of nanostructure and pinning properties in solution deposited YBa2Cu3O7−x nanocomposites with preformed perovskite nanoparticles

Solution deposited YBa2Cu3O7−x (YBCO) nanocomposites with preformed nanoparticles represent a promising cost-effective approach for superior critical current properties under applied magnetic fields. Nonetheless, the majority of YBCO nanocomposites with high nanoparticle loads (>20%) suffer from nanoparticle coalescence and degraded superconducting properties. Here, we study the influence of nanoparticle concentration (0–25% mol), size (5 nm–10 nm) and composition (BaHfO3, BaZrO3) on the generation of structural defects in the epitaxial YBCO matrix, key parameter for vortex pinning. We demonstrate that flash-heated superconducting nanocomposites with 20 mol% preformed BaHfO3 or BaZrO3 perovskite secondary phases feature discrete and small (7 nm) nanoparticles and high density of YBa2Cu4O8 (Y248) intergrowths. We identify a synergy between Y248 intergrowth density and small nanoparticles to increase artificial vortex pinning centers. Also, we validate the multideposition process to successfully increase film thickness of epitaxial nanocomposites with competitive critical currents Ic at 77 K.All authors acknowledge the EU (EU-FP7 NMP-LA-2012-280432 EUROTAPES project), MINECO (COACHSUPENERGY, MAT2014-51778-C2-1-R) and Generalitat de Catalunya (2017SGR1519 and Xarmae). ICMAB authors acknowledge the Center of Excellence award Severo Ochoa SEV-2015-0496. Authors acknowledge the Scientific Services at ICMAB, the ICN2 Electron Microscopy Division and LMA-INA for offering access to their instruments and expertise. J.G. and M.C. also acknowledge the Ramon y Cajal program (RYC-2012-11709 and RYC-2013-12448 respectively). Z.L. acknowledges the China Scholarship Council (CSC).Peer reviewe

Intrinsic anisotropy versus effective pinning anisotropy in YBa2Cu3O7 thin films and nanocomposites

The intrinsic and effective anisotropies, both in the liquid and solid vortex regimes, of YB a 2 C u 3 O 7 (YBCO) pristine and nanocomposite thin films have been investigated. Angular resistivity measurements under varying fields and temperatures were performed to characterize the intrinsic vs effective anisotropy of samples in the regime of long-range vortex displacements. The effective anisotropy γ eff was determined from the scaling of the irreversibility line, applying the Blatter approach developed for uniaxial anisotropic superconductors. Resistive measurements in flux flow were utilized, in addition to H c 2 measurements in ultrahigh-fields, to determine the intrinsic anisotropy mass γ, enabling the study of a large number of samples with varied nanoparticle compositions. In order to access the intrinsic anisotropy in the vortex solid phase, complex impedance measurements at high microwave frequencies were performed, allowing us to access the flux-flow intrinsic anisotropy in the regime of very short vortex oscillations within the pinning potential wells. Results show that while the effective anisotropy γ eff decays as the nanoparticles-induced nanostrain in the YBCO films increases, the intrinsic anisotropy γ (determined both in dc and at microwave frequency) remains unaltered.Peer reviewe

Vortex pinning properties at dc and microwave frequencies of YBa2Cu3O7-x films with nanorods and nanoparticles

YBa2Cu3O7−x (YBCO) nanocomposites for wire applications need to operate in a broad range of frequencies, ranging from dc in magnets to GHz in cavities and screenings of future particle accelerators. We have investigated the in-field and angular vortex pinning performance in dc and at 50 GHz of two types of nanocomposites, pulsed laser deposition (PLD) YBCO with mixed Ba2YNbO6 + Ba2YTaO6 (BYNTO) nanorods and chemical solution deposited (CSD) YBCO with BaHfO3 (BHO) nanoparticles (NPs), and the pristine counterpart films, grown on top of single-crystalline substrates. Transport measurements performed up to 9 T between 5 and 77 K show that CSD nanocomposites exhibit a smooth field decay and increased single-to-collective crossover field H* compared to pristine samples, associated to the enhanced isotropic pinning contribution induced by the NPs, while PLD films exhibit unchanged H* and superior critical current densities up to higher irreversibility fields, associated to the anisotropic contribution introduced by the rods. Microwave in-field measurements of the pinning constant kp revealed CSD NCs exhibit a qualitatively similar, but smoother kp(H) than pristine samples, whereas for PLD samples, a growing kp(H) dependence is observed as a result of the increased relevance of the stiffness of the fluxons pinned by nanorods.This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom Research and Training Programme 2014–2018 and 2019–2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. We acknowledge financial support from Spanish Ministry of Economy and Competitiveness through the Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496), SUMATE project RTI2018-095853-B-C21, cofinanced by the European Regional Development Fund, COST-Nanocohybri CA16218, DWARFS project (MAT2017-83468-R) and Catalan Government with 2017-SGR-1519 and XRE4S.Peer reviewe

Epitaxial YBa2Cu3O7−x nanocomposite films and coated conductors from BaMO3 (M = Zr, Hf) colloidal solutions

Superconducting nanocomposites are the best material choice to address the performance required in power applications and magnets working under high magnetic fields. However, it is still challenging to sort out how to achieve the highest superconducting performance using attractive and competitive manufacturing processes. Colloidal solutions have been recently developed as a novel and very promising low cost route to manufacture nanocomposite coated conductors. Well dispersed and stabilized preformance nanoparticle solutions are first prepared with high concentrations and then mixed with the YBa2Cu3O7 metalorganic precursor solutions to generate colloidal solutions to grow the nanocomposite films. Here we demonstrate, for the first time, that non-reactive BaZrO3 and BaHfO3 perovskite preformed nanoparticles are suitable for growing high quality thin and thick films, and coated conductors with a homogeneous distribution and controlled particle size using this fabrication method. Additionally, we extend the nanoparticle content of the nanocomposites up to 20%–25% mol without any degradation of the superconducting properties. Thick nanocomposite films, up to 0.8 μm, have been prepared with a single deposition of low-fluorine solutions using an ink jet printing dispenser and we demonstrate that the preformed nanoparticles display only a very limited coarsening during the growth process and so high critical current densities J c (B) under high magnetic fields. These films show the highest critical currents achieved so far based on the colloidal solution approach, I c = 220 A/cm-w at 77 K and self-field, and they still have a high potential for further increase in the film thickness. Finally, we also show that nanocomposite YBa2Cu3O7–BaZrO3 coated conductors based on an alternating beam assisted deposited YSZ buffer layer on stainless steel metallic substrates can be developed based on these novel colloidal solutions. Non-reactive preformed oxide perovskite nanoparticles are therefore very promising elements to further advance the colloidal solution approach in the implementation of low cost and high performance coated conductors for high magnetic field applications.All authors acknowledge the EU (EU-FP7 NMP-LA-2012-280432 EUROTAPES project), MINECO (COACHSUPENERGY, MAT2014-51778-C2-1-R and SUPERINKS, RTC-2015-3640-3) and Generalitat de Catalunya (2014SGR 753 and Xarmae). ICMAB authors acknowledge the Center of Excellence award Severo Ochoa SEV-2015-0496. TEM microscopy work was conducted in the Catalan Institute of Nanoscience and Nanotechnology (ICN2). Authors acknowledge the ICN2 Electron Microscopy Division for offering access to their instruments and expertise. Part of the STEM microscopy work was conducted in 'Laboratorio de Microscopias Avanzadas' at the Instituto de Nanociencia de Aragon-Universidad de Zaragoza. Authors acknowledge the LMA-INA for offering access to their instruments and expertise. JG and MC also acknowledge the Ramon y Cajal program (RYC-2012-11709 and RYC-2013-12448, respectively). ZL and BM acknowledge the China Scholarship Council (CSC) and F I MINECO for fellowships, respectively.Peer reviewe