In this presentation I will show how different types of particle irradiations can markedly enhance the in-field critical current in commercial 2^nd generation superconducting tapes, and that, by selecting the type of irradiation, this enhancement can be applied to fully processed industrial production tapes without any modification of the growth process.

Tremendous improvements have been made during the past decade in the performance of high temperature superconducting wire based on YBa₂Cu₃O_7−δ (YBCO). Superconducting wire is becoming competitive for space-limited and weight-limited applications: several projects involving urban grid, transformers, compact motors or offshore wind turbines are being developed or deployed worldwide. However, widespread deployment of superconduction cables in the electric power grid has been hindered by the high fabrication cost, while in-field coil-based applications struggle with the rapid fall of the critical current in an external magnetic field.

The large critical current densities (J_c) in these wires, now >3 MA/cm² at 77 K self-field, are achieved by strict control over the micro- and nanostructures. The current manufacturing process involves a complex combination of highly engineered buffer layers for epitaxy, and controlled formation of defects such as dislocations, stacking faults, rare-earth nanoparticles and BaZrO₃ nanorods, that act as vortex pinning centers.

Irradiation can be used to independently induce defects with well-controlled density and topology (point, cluster, column). Recently, we found very promising synergies between such defects and the preexisting pinning structure of YBCO based tapes. Crossed heavy-ion irradiations at 1.4 GeV reduce the anisotropy of J_c to ~1.3, while irradiations with light ions, such as 4 MeV protons and 6 MeV oxygen, double or triple J_c in fields of 3 to 6T. The optimal irradiation dose for maximum J_c is temperature and field dependent; large-scale time dependent Ginzburg-Landau simulations yield a good description of our results.

Irradiation of fully processed tapes with light ions requires exposure times of just a few tens of seconds per cm², with relatively low beam currents. If higher beam currents were used, irradiation times could be reduced to levels required for a reel-to-reel manufacturing process.

This work was supported by the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the U.S. D.O.E., Office of Science, Office of Basic Energy Sciences and by the D.O.E, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357

Long-length GdBCO coated conductors (CCs) possessing high critical current at 77 K in self field up to ~800 A/cm-width are being produced via a reactive co-evaporation deposition and reaction (RCE-DR) process by SuNAM Co. in Korea. Due to a very high conversion rate from an amorphous precursor film into the GdBCO film, an overall processing speed for producing the GdBCO film is faster than 120 m/h [J. H. Lee et al., Supercond. Sci. Technol. 27 (2014) 044018]. While this technology has been continuously improved by SuNAM for higher performance GdBCO CCs, a relatively weak pinning property has been the most challenging problem [Choi et al., IEEE Trans. Appl. Supercond. 23 (2013) 8001004]. Thus, in order to overcome this problem, we have tried to refine Gd₂O₃ particles trapped in the GdBCO matrix, and also to produce defects by a post-annealing process in a low oxygen pressure. While refinement of Gd₂O₃ particles, enabled by an optimal processing, was turned out to be very effective for J_c improvement in all field directions, representing the isotropic pinning effect, generation of stacking faults aligned along the c-axis of GdBCO, formed by the post annealing process, were found to be very effective for J_c improvement for the field parallel to the c-axis like columnar defects or nanorods. In this talk, detailed pinning effects of theses pinning centers will be presented for a discussion.

This work was supported by the Power Generation and Electricity Delivery of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Trade, Industry and Energy (No. 20131010501800).

In Ba₂YNbO₆ (BYNO) - added YBCO films grown by pulsed laser deposition at 800°C, we explored the influence of off-stoichiometric YBCO starting target compositions. We found that order of magnitude higher growth rates (~ 5 - 10 nm·s^-1 compared to <1 nm·s^-1 for standard films) led to excellent J_c(B) behaviour. The off-stoichiometric starting composition was consistent with the presence of liquid during the growth. J_cs (77 K, 1 T) of ~ 1.2 MA·cm^-2 (B||a-b) and ~ 0.5 MA·cm^-2 (B||c) were measured in 0.5 micron thick films, grown in only in < 1 minute. TEM showed truncated BYNO nano-columns with densities of ~ 20 and lengths of ~ 50 nm. Comparator films containing the same BYNO pinning additions but without use of the off-stoichiometric starting composition had lower J_cs of 0.2 MA·cm^-2 (B||a-b) and ~0.4 MA·cm^-2 (B||c), even at low growth rates of ~ 1 nm·s^-1.

The authors acknowledge funding from EUROTAPES, a collaborative project funded by the European Community's Seven Framework Programme (FP7 / 2007 - 2013) under Grant Agreement n.280432.

The incorporation of inert metal oxide nanocrystals in YBa₂Cu₃O_7-x (YBCO) coated conductors can lead to a better J_C dependence on the magnitude and orientation of the magnetic field, making high field applications possible. In this work, we make use of preformed nanocrystals (PNCs) as artificial pinning centers that are added to the YBCO precursor solution. The use of PNCs offers the promise of a better control over particle growth, size, size distribution and shape compared to nanocrystals that are formed during the YBCO processing.
We synthesized ZrO₂ and HfO₂ nanocrystals (NCs) of 7 nm and a narrow size distribution. The NCs are initially capped with hydrophobic ligands, ensuring colloidal stability in apolar solvents. However, as the YBCO precursor typically provides a more polar environment, e.g., methanol, an important aspect of this research involves ligand exchange and the appropriate stabilization procedure. We are able to stabilize the NCs in high concentration for at least 2,5 months in a TFA-YBCO precursor solution, confirmed by dynamic light scattering analysis.
Afterwards, the YBCO-PNCs suspensions were deposited on a LaAlO₃ substrate through spin-coating to study the influence of the NCs in the YBCO coating. The effect of different concentrations of pinning centers in YBCO was investigated, leading to a critical current density J_C of 4.5 MA/cm² at 77K in self-field, compared to a J_C of 3.8 MA/cm² of pristine YBCO, a better dependency of J_C versus the applied magnetic field and a pinning force increase by a factor 12 at high magnetic fields.
This new, successful approach of the incorporation of preformed nanocrystals in CSD coatings holds the promise to the effective and economically efficient application of high-temperature superconductors in high and alternating magnetic field applications, relevant in alternative energy generation.

This work was financially supported by Ghent University and Eurotapes, a collaborative project funded by the European Community’s Seven Framework Program (EU-FP7 NMP-LA-2012-280432).

So far, YBa₂Cu₃O_7-x (YBCO) or related compounds are the most promising materials for the realization of coated conductor application. Significant effort was made within the last years to develop biaxial texture templates for such conductors, which can be manufactured in long length. One major approach is the application of ion beam based methods for the preparation of cube textured buffer layers on arbitrarily textured metal tapes as for example the ion beam assisted deposition (IBAD) or alternating beam assisted deposition (ABAD).
We deposited YBCO layers with a thickness of 1 µm and above on TiN buffered IBAD-MgO as well as on ABAD-YSZ templates using pulsed laser deposition. Additionally, artificial pinning centers such as BaHfO₃ (BHO) and the mixed double-perovskite Ba₂Y(Nb/Ta)O₆ (BYNTO) where incorporated in these YBCO layers. X-ray diffraction confirmed epitaxial growth of the superconductor on these templates and biaxially oriented incorporation of the pinning centers in the YBCO matrix. Detailed TEM studies revealed the size and distribution of the nanoparticles. A critical current density J_c of more than 2 MA/cm² was determined at 77 K in self-field for 1 µm thick films. Transport measurements were performed in order to study the anisotropy of J_c in magnetic fields. The influence of the deposition conditions on the distribution of artificial pinning centers and the resulting transport properties will be discussed in detail.

The authors acknowledge financial support from EUROTAPES, a collaborative project funded by the European Union's Seventh Framework Programme (FP7 / 2007 - 2013) under Grant Agreement no. 280432.

Superconducting YBCO coated conductors are excellent materials for high efficient and energy saving providing strategic opportunities for the new grid paradigm of the XXI century. Low cost manufacturing is however one of the most stringent requirements. For that purpose, strong efforts are being devoted to decrease cost in scalable processes and the combination of chemical solution deposition (CSD) and ink jet printing (IJP) techniques is a key player.
We will report on our successful efforts in growing YBCO films and coated conductors by CSD using low fluorine solutions (80% fluorine reduction with respect to the all-TFA route) with special emphasis in thick film growth (micron range) by IJP deposition.
Upon an intensive work on pyrolyzing thick IJP films, we have grown thick (~1µm) films optimizing growth conditions and growth rate. Standard growth rates (0.8 nm/s) have been increased up to 2.3 nm/s in single deposited IJP YBCO layers. We have identified a tendency of these thick single deposited films to segregate second phases, which needed to be minimized by optimizing growth parameters and rate, in order to obtain high performance films above 2 MA/cm2 at 77 K.
When this YBCO films are grown on flexible metallic tapes, CZOMOD/YSZABAD/SS, the typical reactivity between CeO2-based buffer layers and YBCO was avoided by minimizing growth temperatures with proper tuning of supersaturation conditions and solution formulation.
All these knowledge has been transferred to the growth of thick YBCO nanocomposites with BaZrO3 and Ba2YTaO6 nanoparticles, demonstrating the potentiality of all CSD coated conductors.
Advanced HRTEM, STEM-EELS, FIB-cross sections, x-ray and angular dependent transport measurements were extremely valuable for the understanding and optimization of the performances.

The research leading to these results has received funding from EU-FP7 NMP-LA-2012-280432 EUROTAPES project, MP1201 Cost action and MAT2014-51778-C2-1-R national project.

The TFA-MOD (metal-organic deposition using trifluoroacetates) process is a low-cost non-vacuum process for fabricating YBCO (YBa₂Cu₃O_7-x) superconducting tape. However, it also requires vacuum processes for preparation of oriented intermediate layers and oriented metal substrate. These vacuum processes substantially raise the production cost for TFA-MOD. We propose a new process to eliminate these expensive vacuum processes. The architecture is YBCO superconductor (non-vacuum TFA-MOD) / oriented origin (non-vacuum process) / non-oriented oxide barrier layer (vacuum process, but low cost) / non-oriented metal substrate (as is). Furthermore, potential in-plane alignment (delta phi) of the YBCO superconducting layer may be below 1 degree.
One of the important phenomena for realizing the above-mentioned new architecture is transition of the oriented layer from on the oriented oxide strip toward on the non-oriented area. We partially covered LaAlO₃ with Pt, which is not lattice-matched to YBCO superconductor. From the edge of LaAlO₃, highly oriented YBCO is observed on Pt layer 5 microns from the edge. 10 microns from the edge, orientation is still confirmed by diffraction pattern of YBCO layer. 20 microns from the edge, orientation of YBCO is weak. From the results, provided oriented oxide strips are placed every 10 microns, we can obtain oriented YBCO superconducting layer having delta phi below 1 degree by TFA-MOD.
These results suggest the possibility of establishing an extremely low-cost process for TFA-MOD in the future.

The development of low-cost techniques for the growth of high performance YBCO coated conductors is one of the major requirements in obtaining a widespread use of superconductivity in large scale applications. Among all the techniques, chemical solution deposition (CSD) has become a very competitive cost-effective and scalable methodology to produce epitaxial thin films. Using trifluoroacetate precursors, high performance superconducting films can be obtained without carbon retention.
However, the reaction of the nanocrystalline oxide and fluorinated intermediates under a humid atmosphere limits the growth rate and has tight requirements in the gas flow control thus becoming very cumbersome to achieve at large scale a high production throughput. We have developed a new CSD approach using non-Fluorine metalorganic precursors which has less restricted gas flow conditions to form epitaxial YBCO films. Several fluorine-free metalorganic solutions and processing conditions have been analysed together with different strategies to enhance the decomposition of the barium carbonate forming as an intermediate phase to avoid the retention of carbon impurities in the epitaxial YBCO thin films. We will present how two novel processing procedures can be efficiently combined to reach this goal: rapid thermal annealing and heating under reduced pressure. Thermogravimetric analysis, Evolved Gas Analysis, X-ray diffraction and infrared measurements were used to control the intermediate phases leading to epitaxial growth of the films.
On the other hand, extensive research exploring different regions of the phase diagram has been carried out in order to control the nucleation process in order to obtain epitaxial growth at the maximum growth rate. Several processing parameters, such as total pressure, oxygen pressure, heating ramps and growth temperatures, were investigated. We have succeeded in obtaining highly epitaxial YBCO thin films of 200-500nm under processing conditions which make these films very promising for coated conductor applications. SQUID and transport measurements have shown that high critical temperatures (Tc=90-92K) and critical current densities (Jc=3MA/cm2 at self-field and 77 K) can be obtained with very appealing film microstructures comparable to high quality standard TFA films.

The research leading to these results has received funding from EU-FP7 NMP-LA-2012-280432 EUROTAPES project, MAT2011-28874 national project. L.S. and  Ministerio español de Educación, Cultura y Deporte para la Formación de Profesorado Universitario.