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We have simulated the inductive critical currents and transport currents in the dissipative state of superconducting thin films with an increasing amount of porosity by using a Bean model-based programme (Trazacorrientes®) and finite-element software. Simulations allowed us to find a quantitative, quasi-universal relationship between the overall critical current density and the normal-state resistivity via the sample porosity. This theoretical curve served to fit the experimental data found for a large number (?150) of epitaxial YBa2Cu3O7?xthin films grown by the trifluoracetate route. [ABSTRACT FROM AUTHOR]

Superconducting YBa2Cu3O7 (YBCO) thin films were grown by the trifluoroacetates route onto metallorganic deposited La0.7Sr0.3MnO3 (LSMO) buffer layers. The growth conditions of the LSMO films have been studied in detail and fully strained epitaxial layers with atomically flat surfaces have been obtained with local roughness [?]1 nm, as determined by atomic force microscopy. We prove that this surface morphology is a key parameter for achieving YBCO/LSMO multilayers with high critical current densities in self-field, Jcsf (77 K) = 1.8 MA cm[?]2. Angular pinning studies demonstrate that the defect structure is modified with respect to standard TFA-YBCO films as a pronounced peak in Jc is observed for H\parallel c at high temperatures. This indicates the presence of anisotropic defects playing an important role in vortex pinning even at the irreversibility line stressing the suitability of these all-chemical TFA-YBCO/LSMO multilayers as conductive coated conductor architectures. [ABSTRACT FROM AUTHOR]

Tuning the interfacial area is essential for the optimization of nanostructured CeO2 in a variety of applications. In this work, we investigate the microstructural mechanism of an oxidation-induced transition from a partially oriented, granular and porous nanostructure to a dense epitaxial one in CeO2 films deposited from chemical solutions. Crystallization under reducing atmospheric conditions results in a nanometric granular microstructure with a high fraction of C decorating grain boundaries and interstitial cavities. Annealing in oxidizing conditions removes C impurities and promotes grain growth, resulting in a fully epitaxial film, as well as stabilizing the otherwise energetically prohibitive polar (001) planes. A mechanism that considers an impurity induced grain boundary blocking mechanism and the stabilization of (001) planes via surface oxidation is proposed. [ABSTRACT FROM AUTHOR]

Anisotropy is an intrinsic factor that dictates the magnetic properties of YBa2Cu3O7−δ and therefore has a great impact on many applications. Artificial pinning centres are often introduced in an attempt to mitigate its effect, resulting in less anisotropic electrical and magnetic properties. However, the nanoengineering of superconductors makes the quantification of the anisotropy itself uncertain: the intrinsic anisotropy due to the layered structure, quantified by the anisotropy factor γ, mixes with the additional anisotropy due to pinning. As a consequence, there is no consensus on the experimental anisotropy factor γ that can result in YBa2Cu3O7−δ when directional (twin planes, nanorods) or isotropic defects are present. We present measurements of the magnetic field and angular dependent surface impedance in very different nanostructured YBa2Cu3O7−δ films, grown by a chemical route and by pulsed laser deposition with different kind of defects (nanorods, twin planes, nanoparticles). We show that the surface impedance measurements are able to disentangle the intrinsic anisotropy from the directional pinning anisotropy, thanks to the possibility of extracting the true anisotropic flux–flow resistivity and by correctly exploiting the angular scaling. We find in all films that the intrinsic anisotropy γ = 5.3 ± 0.7. By contrast, the pinning anisotropy determines a much more complex, feature–rich and nonuniversal, sample–dependent angular landscape. [ABSTRACT FROM AUTHOR]

The achievement of high critical currents in ‘all-chemical’ YBa2Cu3O7−δ thick films from low cost and versatile chemical solution deposition (CSD) methodology is still an open issue. Here we report a study of the nucleation and growth conditions to achieve YBa2Cu3O7−δ films in excess of 1 micron using single pass inkjet printing or multideposition of low-fluorine metalorganic precursors. Growth conditions of thick YBa2Cu3O7−δ layers are first investigated on LaAlO3, where there is no interfacial chemical reactivity. The second architecture investigated is an ‘all-chemical’ CSDCe0.9Zr0.1O2(CZO)/YSZ multilayer on single crystal substrates which serves as model system for coated conductors. Finally, the ‘all-chemical’ coated conductor architecture CSDYBa2Cu3O7/CSDCZO/ABADYSZ/stainless steel, where ABAD stands for alternating beam assisted deposition, is investigated. The nucleation conditions of YBa2Cu3O7−δ films on top of CΖΟ cap layers have been selected to minimize the formation of the BaCeO3 phase at the interface. We demonstrate that by combining the use of Ag additives in the starting YBCO solution and processing conditions leading to low supersaturation (high water pressure and low temperature) we can achieve ∼1 μm thick YBa2Cu3O7−δ films and coated conductors with high critical currents of = 390 and 100 A/cm-w, respectively, at 77 K and self-field. The achieved control of the interfacial reactivity with CeO2 cap layers opens a route for further increasing film thickness and critical currents in ‘all-chemical’ YBa2Cu3O7−δ coated conductors. [ABSTRACT FROM AUTHOR]

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 Jc(B) under high magnetic fields. These films show the highest critical currents achieved so far based on the colloidal solution approach, Ic = 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. [ABSTRACT FROM AUTHOR]

In-field angular pinning performances at different temperatures have been analysed on chemical solution deposited (CSD) YBa2Cu3O7−x (YBCO) pristine films and nanocomposites. We show that with this analysis we are able to quantify the vortex pinning strength and energies, associated with different kinds of natural and artificial pinning defects, acting as efficient pinning centres at different regions of the H–T phase diagram. A good quantification of the variety of pinning defects active at different temperatures and magnetic fields provides a unique tool to design the best vortex pinning landscape under different operating conditions. We have found that by artificially introducing a unique defect in the YBCO matrix, the stacking faults, we are able to modify three different contributions to vortex pinning (isotropic-strong, anisotropic-strong, and isotropic-weak). The isotropic-strong contribution, widely studied in CSD YBCO nanocomposites, is associated with nanostrained regions induced at the partial dislocations surrounding the stacking faults. Moreover, the stacking fault itself acts as a planar defect which provides a very effective anisotropic-strong pinning at H//ab. Finally, the large presence of Cu–O cluster vacancies found in the stacking faults have been revealed as a source of isotropic-weak pinning sites, very active at low temperatures and high fields. [ABSTRACT FROM AUTHOR]

An attempt to grow a thin epitaxial composite film of YBa2Cu3O7−δ (YBCO) with spinel MnFe2O4 (MFO) nanoparticles on a LAO substrate using the CSD approach resulted in a decomposition of the spinel and various doping modes of YBCO with the Fe and Mn cations. These nanostructural effects lead to a lowering of Tc and a slight Jc increase in field. Using a combination of advanced transmission electron microscopy (TEM) techniques such as atomic resolution high-angle annular dark field scanning TEM, energy dispersive x-ray spectroscopy and electron energy-loss spectroscopy we have been able to decipher and characterize the effects of the Fe and Mn doping on the film architecture. The YBaCuFeO5 anion-deficient double perovskite phase was detected in the form of 3D inclusions as well as epitaxially grown lamellas within the YBCO matrix. These nano-inclusions play a positive role as pinning centers responsible for the Jc/Jsf (H) dependency smoothening at high magnetic fields in the YBCO-MFO films with respect to the pristine YBCO films. [ABSTRACT FROM AUTHOR]

We present our work in the preparation of metallorganic precursor solutions with reduced fluorine content, able to fulfil the requirements for high-performance superconducting YBCO epitaxial layers as a promising approach to low cost and scalable coated conductors. Six different solutions using different quantities of fluorine and non-fluorine carboxylate precursors with a total amount of fluorine from 10 to 50% that of standard trifluoroacetic acid (TFA) solutions. For stabilization purposes different coordinating agents have been used and the solution rheology has been modified for proper substrate wettability. Thermal decomposition analysis and infrared spectroscopy performed directly in films, have revealed that the decomposition takes place in two consecutive stages around 265 and 310 °C respectively, and nuclear magnetic resonance (NMR) analysis could unveil the chemical reactions taking place in the solution. Using the solutions with 20% fluorine and upon optimization of the growth process parameters, YBCO layers with Tc and Jc(77 K) of 90 K and 4 MA cm−2 are obtained. [ABSTRACT FROM AUTHOR]

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 YBa2Cu3O7 (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 CeO2 and ZrO2 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 (Jc ∼ 3–4 MA cm−2 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. [ABSTRACT FROM AUTHOR]

High temperature superconducting (HTS) wires require a detailed characterization of the possible degradation of their properties by handling at room temperature as well as during their service life, establishing the limits for associated functional devices and systems. In this paper, we study the mechanical behavior of spliced joints between commercial HTS coated conductors based on YBCO at room (300 K) and service temperatures (77 K). Single lap shear tests were performed and the evolution of the critical current and electric resistivity of the joints were measured. The complete strain field for the tape and joints was also obtained by digital image correlation. In addition, tensile tests under an external magnetic field were performed, and the effect of the applied field on the critical current and electric resistivity of the joints were studied. Finally, finite element simulations were employed to reproduce the distribution of the stress field developed in the spliced joint samples during axial loading. [ABSTRACT FROM AUTHOR]

In this work, we have studied by means of in situ electrical measurements the nucleation, growth and sintering stages of epitaxial YBa2Cu3O6+δ (YBCO) superconducting thin films prepared using a chemical solution deposition approach based on metal-organic trifluoroacetate-based (TFA) precursors. Single crystal substrates (LaAlO3 and CeO2/YSZ) were used in this study. Analysis of isothermal time dependences, at different temperatures, of in situ electrical resistance of films allowed to evidence that the growth rate G is strongly temperature dependent, i.e. G is enhanced by a factor ∼15 when going from 700 to 810 °C. Additionally, we demonstrate that adding Ag-TFA in the solution may enhance the growth rate by as much as 50%, as compared to pure YBCO, thus confirming previous assessments of the strong influence of Ag doping on YBCO film growth and microstructure. In situ electrical resistance measurements show as well that an incubation time exists and we infer the origin of its temperature dependence. Finally, a thermodynamic analysis allows proposing a single equation for the growth rate of YBCO films integrating all the relevant processing parameters. Our analysis has validated the solid-gas reaction-diffusion model describing the growth of YBCO films from TFA precursors and thus enlarges the knowledge required to enhance the control of the microstructure and superconducting properties of solution-derived YBCO films. [ABSTRACT FROM AUTHOR]

We study the effect of twin boundaries (TBs) on the critical current density of YBa2Cu3O (YBCO) films and nanocomposites grown on different substrates. Varying both the direction of the current and magnetic field, we show that the TB orientation is a crucial parameter to consider in the optimization of Jc for particular applications. A quantitative and detailed analysis of the role of TBs on vortex dynamics has allowed us to infer that extended TB planes in pristine YBCO films can reduce Jc by 60% at low temperatures due to vortex channeling effects or increase it by a 98% at high temperatures due to directional vortex pinning. Moreover, we demonstrate that TB length and distribution can be strongly modified in YBCO nanocomposites. We observe that TB planes with no vertical coherence are still effective for vortex pinning while are not to create channels for easy vortex flow. [ABSTRACT FROM AUTHOR]

Vortex creep in YBa2Cu3O7 − x (YBCO) films grown from the trifluoracetate (TFA) chemical route with BaZrO3 and Ba2YTaO6 second-phase nanoparticles (NPs) has been investigated by magnetic relaxation measurements. We observe that in YBCO nanocomposites the phenomenological crossover line from the elastic to the plastic creep regime is shifted to higher magnetic fields and temperatures. The origin of this shift lies on the new isotropic-strong vortex pinning contribution appearing in these nanocomposites, induced by local lattice distortions. As a consequence, we demonstrate that the addition of non-coherent NPs produces a decrease in the creep rate S in most of the phase diagram, particularly, in the range of fields and temperatures (, ) relevant for large scale applications. [ABSTRACT FROM AUTHOR]

Magnetic Hall probe microscopy in combination with an inverse problem solver was used to simultaneously determine the intragranular and intergranular critical current density dependences on the applied field of YBCO melt-textured welds with [001]-misorientation angles from 0° to 30°. This methodology enabled us to investigate the pinning mechanisms of grain boundary vortices, which evolve from Abrikosov vortices (AVs) to Abrikosov-Josephson vortices (AJVs) and then to Josephson vortices (JVs) as the angle increases. We present a magnetic field versus grain boundary angle phase diagram at 77 K in which different intergrain vortex motion regimes can be identified. [ABSTRACT FROM AUTHOR]

A novel mechanism based on aliovalent doping, allowing fine tuning of the nanostructure and surface topography of solution-derived ceria films, is reported. While under reducing atmospheric conditions, non-doped ceria films are inherently polycrystalline due to an interstitial amorphous Ce2C3 phase that inhibits grain growth, a high quality epitaxial film can be achieved simply by doping with Gd3+ cations. Gd3+ \leftrightarrow Ce4+ substitutions within the lattice are accompanied by charge-compensating oxygen vacancies throughout the volume of the crystallites acting as an efficient vehicle to reduce the barrier for grain boundary motion caused by interstitial Ce2C3. In this way, the original nanostructure is self-purified by pushing the amorphous Ce2C3 phase towards the free surface of the film. Once a full epitaxial cube-on-cube oriented ceria film is obtained, its surface morphology is dictated by the interplay between faceting on low energy {110} and/or {111} pyramidal planes and truncation of those pyramids by (001) ones. The development of the latter requires the suppression of their polar character which is thought to be achieved by charge compensation between the dopand and oxygen along \langle 100\rangle directions. [ABSTRACT FROM AUTHOR]

Rectified flux motion arising from the collective effect of many interacting vortices is obtained in a specially designed superconducting device. Ratchet structures with different asymmetric pinning potentials are generated by tuning the size, depth, and distribution of triangular blind-antidots in a high-temperature superconducting film. We experimentally and theoretically demonstrate that the amplitude and sign of the rectified vortex motion can be finely tuned with the pattern geometry. Two different dynamical regimes depending on the nature of vortices initiating the dissipation are identified, which can control the rectified vortex motion.