Final Report Summary - EUROTAPES (European development of Superconducting Tapes: integrating novel materials and architectures into cost effective processes for power applications and magnets.)
Executive Summary:
European researchers and industrial companies have joined forces within EUROTAPES to make progress towards providing long length substrates for use in high current Superconducting (SC) tapes, using both vacuum deposition techniques (Pulsed Laser Deposition, PLD) and chemical (Chemical Solution Deposition, CSD) methods for the multilayer growth of coated conductors (CCs) based on REBa2Cu3O7 (RE=Y, Gd; REBCO). Development of novel nanostructuring approaches has allowed to achieve improved performance at high and ultrahigh magnetic fields while progress in manufacturing control has pushed CCs industry to make possible the power applications of superconductivity.
The overall goal was to decrease the cost/performance ratio (down to ~100 €/kA-m) of the CCs, as measured by the cost of fabricating 1 m of conductor, 1 cm wide divided by the critical current Ic at 77 K. The combination of high performance (large Ic) with a high production volume has been shown to make feasible this goal.
The concept of EUROTAPES has been to integrate the advanced materials developments into longer length CCs and to generate the process and control system know-how necessary to move into production. The best combination of the physical and chemical methods has been used with two types of substrates: Alternate Beam Assisted Deposition (ABAD)-coated stainless steel and biaxially textured Ni-W Rolling Assisted Biaxial Texturing (RABiTTM).
Two CCs architectures have be chosen for ‘a demonstration stage’: ABAD-PLD approach (lengths in excess of 600 m) and RABiT-CSD approach (CCs longer than 300 m).
Manufacturing developments, including definition of quality assurance and quality control methods, have been one of the focus of the project. Both of these thrusts have been underpinned by advanced characterization and measurements with nanostructural (Scanning Transmission Electron Microscopy) and high magnetic field transport and magnetic properties.
The CCs targets several final uses: i/ cables, transformers and fault current limiters running at high temperatures (~77K) and self-field; ii/ motors/generators, magnets and SMES (Superconductor Magnetic Energy Storage) working at high magnetic fields (3-10T) and intermediate temperatures (30-60K) and iii/ magnets for NMR, fusion, compact accelerators and High Energy Physics working at low temperature (~5K) and ultra-high magnetic fields (>20T).
The main scientific and technological advances achieved are:
• Simplified metallic substrates cost-effectively planarized by chemical methods for ABAD templates.
• New metallic non-magnetic (Ni and Cu based) substrates with reduced magnetic AC losses.
• Preparation methods of stable alcoholic solutions of well dispersed oxide nanoparticles with tuned size useful for a novel route of nanocomposite thin film growth.
• Low Fluorine content eco-friendly colloidal solutions, with preformed nanoparticles, used to grow high current nanocomposite CCs by CSD based on Ink Jet Printing.
• Development of processes to prepare engineered nanocomposite CCs using CSD or PLD with very high pinning forces and Ic at high and ultrahigh magnetic fields based on thorough knowledge on the relationship among nanoscale defects and vortex pinning. A worldwide record performance in long length CCs working at 4.2 K and 18 T has been achieved.
• A new round wire conductor architecture (CORT, Conductor-in-Round-Tube) which can be adapted to design compact cables with improved transport capability.
• Improved high throughput processing methodologies with high yields and performance and the cost / performance metric required for market penetration, including implementation of in-situ and ex-situ continuous quality control tools based on optical and Hall mapping of CCs for the fabrication and testing.
• The convincing demonstration of the scalability of coated conductor manufacturing by Bruker through long length production of ABAD CC (+600 m) based on proven advances in materials and PLD processes.
Project Context and Objectives:
The project has focused in developing new routes towards CCs with enhanced performance, higher robustness, simplified conductor architectures and more environmentally friendly chemical processes and quality control tools for enhanced throughput on manufacturing. The overall goal has been to decrease the cost/performance ratio.
The first issue handled by the project was the development of novel features of two conductor architectures: the ABAD and RABiT approaches. In the first case, the main achievement was the use of solution deposition planarization (SDP) to gain CC yield contributing to an important cost reduction. Ink Jet Deposition (IJP) was used to scale-up the SDP production process for this novel ABAD architecture. Concerning RABiT substrates, an important achievement has been the demonstration of the suitability of using Ni 9%atW as a non-magnetic substrate with a high crystalline texture. In both cases adapted robust CSD buffer layers were developed.
Novel eco-friendly (low F) YBCO precursors for low cost CCs based on CSD have been validated to go to a scale-up stage for pristine and nanostructured CCs. A significant achievement has been to demonstrate that inks with a reduction of F content up to 80 % can be used with IJP with a final thickness of 1.2 µm achieved with single deposition and 1.6 µm with double deposition. These compositions have been successfully used in the reel-to-reel IJP route to CCs based on ABAD and RABiT substrates (up to 300 m in length). In the case of ABAD substrates and PLD YBCO deposition CCs in excess of 600 m have been demonstrated with high performance. Quality control tools such as in-situ optical measurements and ex-situ Hall mapping have been implemented to enhance yield and throughput.
Within the objective of creating nanocomposite CCs, the consortium has been very successful creating new approaches based on CSD and PLD. After the use of complex solutions a novel CSD approach was developed based on solution prepared well dispersed preformed nanoparticles with controlled sizes. Once stabilized as colloidal alcoholic inks they can be used for CSD YBCO growth. Suitable compositions (ZrO2, HfO2, BaZrO3, BaHfO3) were found leading to high performance nanocomposite CCs with enhanced control of performance and manufacturing. Highly epitaxial CSD nanocomposite REBCO (RE=Y, Gd) films were grown from complex or colloidal solutions. The main objective of controlling the final size of nanoparticles and defects associated to them (intergrowths, clustered vacancies) to enhance the vortex pinning force has been achieved. The novel colloidal solutions can now be used in the continuous CC reel-to-reel manufacturing process using IJP.
Very significant progress was also made in the development of self-assembled YBCO nanocomposite CCs by PLD based on BaHfO3 (BHO) and Ba2YNb0.5Ta0.5O6 (BYNTO) nanorods and associated defects. Several combinations of double perovskites with Y2O3 and the laser repetition rate were used to tune the pinning landscape at low and high temperatures on single crystalline substrates. The knowledge generated was transferred to metallic substrates and excellent performances demonstrated, particularly, worldwide record values on Ic were achieved at ultra-high magnetic fields and low temperatures on ABAD CCs (Bruker). The whole research activities on the properties of nanostructured CCs was baked with extensive use of advanced superconducting and Scanning Transmission Electron Microscopy investigations which were essential tools to guide in the overall development of high performance nanostructured CCs.
Finally, the project has developed a new type of round wire (CORT, Conductor-in-Round-Tube) based on RABiT or ISD CC tapes helically wound on a 1 mm thick Cu tube with a total diameter of 5 mm. A manufacturing process was defined and it was shown that these wires could lead to breakthroughs in CC applications in various areas of electric power engineering.
Project Results:
1. CHEMICAL SYNTHESIS APPROACH TO STABLE SOLUTIONS OF NANOPARTICLES IN ALCOHOLIC MEDIA
One of the outstanding objectives of EUROTAPES was to create a completely new chemical route to superconducting nanocomposite films based on the use of preformed oxide nanoparticles and colloidal solutions of them with the YBCO metalorganic precursors. This objective required the development of novel methods of oxide nanoparticle preparation with specific oxide compositions being compatible with the YBCO growth. These nanoparticles should fulfill strict requirements in terms of size, they should be highly dispersed and they should be stable in alcoholic media, i.e. the solvents being used in the YBCO solutions. The partners involved in these tasks were UAB, UGENT, ICMAB and TUC.
The colloidal solutions were prepared with high reproducibility using thermal, solvothermal or microwave heating of metallic salts which produced nanocrystals with sizes in the range of 4-10 nm and they had in many cases well developed crystal facets and they remained well dispersed in alcohols. Many different compositions were analyzed and its compatibility with the YBCO growth conditions determined. Several compositions belonging to three different oxide families were prepared: 1/ spinel MFe2O4 (M=Mn, Co) ferrites; 2/ fluorite phases MO2 (M=Ce, Zr, Hf); 3/ perovskite phases BaMO3 (M=Zr, Hf, Ti).
There were two main concerns concerning the behavior of these nanoparticles. One was its stability when a colloidal solution using Y, Ba and Cu metalorganics salts as precursors was prepared; another one was its chemical stability versus the YBCO structure when the film was growing to achieve an epitaxial film. A good stability (several months) of colloidal solutions with high concentration (up to 50 mol %) was achieved in highly ionic TFA and low-F YBCO precursors in all cases. Steric (using Triethylenglycol, nonanoic and decanoic acid ligands) and charge stabilization approaches were followed. All these stable colloidal solutions were used to grow highly epitaxial YBCO nanocomposites.
The second concern of chemical reactivity of the nanoparticles had a strong influence on the desired characteristics and compositions of the selected nanoparticles. Even if a considerable progress was made in improving the chemical compatibility of spinel phases with YBCO (particularly with CoFe2O4), this composition was finally discarded because a certain amount of metal substitution occurred into the YBCO structure reducing the superconducting transition temperature Tc. The fluorite phases were found to be reactive as well, leading to a final formation of perovskite phases BaMO3 (M=Zr, Hf, Ce) but this reaction preserved the superconducting properties of YBCO (Tc was not reduced) because the used metals (Zr, Hf, Ce) do not substitute the Cu positions in the crystalline lattice. A considerable effort was made to control the size, concentration and dispersion of these nanoparticles to analyze the influence of these parameters on the final micro and nanostructure of the YBCO nanocomposites. The main conclusion is that due to the chemical reactivity of the initial fluorite MO2 nanoparticles with the BaF2 formed after the initial decomposition of the Fluorinated precursors there exists always some nanoparticle coarsening and so the final size of the nanoparticles inserted in the YBCO matrix was always larger than the initial ones, i.e. it became cumbersome to keep a full control of the final size of the BaMO3 (M= Zr, Hf, Ce) nanoparticles.
To achieve further control of the final nanoparticles size within the YBCO nanocomposite it was decided to investigate the routes to prepare preformed BaMO3 (M=Zr, Hf, Ti) nanoparticles which we should expect to be non-reactive with the YBCO precursors and, very likely, an additional control of the nanoparticle size, shape, concentration and dispersion should be achieved. The synthesis of the perovskite nanoparticles was made through solvothermal reactions of the corresponding metal hydroxide and alkoxide in a glycol solvent. By selecting the capping ligand it became possible to achieve cube-like nanoparticles with homogeneous dimensions varied in a controlled way within the range of 4-10 nm. The influence of synthesis and washing conditions on the final nanoparticles size, stability and dispersion degree were carefully analyzed when they were exchanged into the YBCO alcoholic solutions. The success of obtaining such perovskite nanoparticles in alcoholic media is a real breakthrough which should have a strong influence on the final competitiveness of the solution colloidal approach to prepare superconducting nanocomposite coated conductors. We have already demonstrated that epitaxial YBCO-BaMO3 (M= Zr, Hf) nanocomposite films have very appealing superconducting performances and also that the process has a strong attractiveness concerning its scalability because the nanoparticle coarsening is very limited. This feature is very important when large film thickness needs to be prepared and so longer thermal annealing times are required.
In conclusion, the success in preparing oxide nanoparticles through solution approaches which can be used in colloidal solutions of YBCO films has been demonstrated for the first time and the attractiveness of this novel methodological approach to prepare complex nanocomposite thin films has been demonstrated. The novel methodology goes well beyond the interest in the area of superconducting materials and it can be certainly extended to many additional functional materials where enhanced performances or multifunctional behavior would become possible.
2. NEW ROUTES TO ADVANCED CSD NANOSTRUCTURED THIN FILMS AND COATED CONDUCTORS
The development of advanced approaches to chemical solution deposition (CSD) of nanostructured YBCO thin films and coated conductors was a highlight of the EUROTAPES project. The main goals were, first of all, to switch from a full use of fluorinated metal-organic precursors of Y, Ba and Cu to new eco-friendly inks with a reduced content of Fluorine. These inks should then be adapted for the use in Ink Jet Printers (IJP) and also to become colloidal solutions incorporating the preformed oxide nanoparticles which should lead to superconducting nanocomposite films and coated conductors. ICMAB and KIT were the main partners involved in this task.
A certain variety of low fluorine (up to 80 % of F reduction) precursors were successfully prepared and its suitability investigated. All the prepared solutions were composed of the same precursor salts (Yttrium trifluoroacetates, Ba and Cu acetates) which were dissolved in mixtures of an alcohol (methanol or butanol) and propionic acid or just propionic acid. Some of them were useful for optimizing the thick film growth process (up to 1.2 µm) using multideposition. Other solutions were optimized to maximize single deposition using IJP (up to 1.1 µm) which could lead to films of 1.6 µm using double deposition. In all cases optimizing the pyrolysis process was an important issue to achieve high reproducibility, a high degree of film homogeneity and a smooth surface. Complementary studies of thermal decomposition and In-situ optical and thermomechanical analysis were extremely useful to achieve wide understanding of the complex film evolution during pyrolysis. All these processes were successfully extended to the case of colloidal solutions using preformed nanoparticles.
Once the process to prepare homogeneous REBCO (RE= Y, Gd) precursor films was completed a wide effort was made to define the optimal conditions to grow epitaxial films with large total critical currents Ic, i.e. with large film thicknesses and high critical current density Jc. Two main difficulties were identified: one is that the degree of supersaturation (and therefore the nucleation and growth rates) in the REBCO growth process changes with film thickness (gas – solid reaction depending on the H2O and HF partial pressures at the growth interface). The second difficulty arises from the fact that it may appear some interfacial reactivity with the CeO2 cap layer mostly used as cap layer in coated conductors. In that case a degraded epitaxy would appear with the corresponding decrease of Jc.
Several strategies were followed to achieve some control of the supersaturation conditions, based on modified parameters (mainly temperature, heating ramp, H2O partial pressure and Ag additives). The largest performances achieved in the CSD route were for a 1.2 µm YBCO film grown on LaAlO3 substrates with Jc(77K)(sf) of 2 MA/cm2 (Ic(77K) = 240 A/cm-width). Values close to those were also achieved in YBCO + BaZrO3 nanocomposites using single IJP deposition: Jc(77K)(sf) = 2.7 MA/cm2 (Ic(77K) = 229.5 A/cm-width). It was also shown that very promising performances can be achieved in (Y,Gd)BCO + BaHfO3 nanocomposite thin films, even if in this case no special efforts were made to enhance the film thickness beyond ~300 nm.
The low F solutions were also widely used to grow YBCO nanocomposites using the preformed nanoparticles approach. Once the MO2 (Zr, Hf) and BaMO3 (M=Zr, Hf) nanoparticles were stabilized with the corresponding inks to form colloidal solutions, it was demonstrated that, essentially, similar growth conditions could be used in the nanocomposite films as compared to the pristine ones, although some fine tuning was always necessary. A particular difficulty to be faced was that the nanoparticles display some tendency to be accumulated at the substrate interface, thus degrading the epitaxial quality. This problem could be solved by using YBCO seed layers which then promote homoepitaxial growth. Typically, YBCO nanocomposite thin films display very high performances at low film thickness (~300 nm): Jc(77K)(sf) = 4-5 MA/cm2 and a smoothed magnetic field dependence as compared to pristine films. Very remarkably, a load record of 20 % M could be achieved with non-reactive BaMO3 (M=Zr, Hf) nanoparticles which then maximize the vortex pinning properties.
Finally, optimizing the growth of REBCO layers on metallic substrates with CeO2 or Ce(1-x)ZrxO2 (CZO) cap layers required dealing with the reactivity issue (BaCeO3 formation through reaction of the cap layer with the BaF2 existing in the film precursor). It was demonstrated that to achieve high quality epitaxy the supersaturation conditions needed to be reexamined in order to maximize the REBCO nucleation rate which competes with the BaCeO3 formation. Here again the nucleation rate depends on the RE ion (Y or Gd) and film thickness and so the processing conditions (Temperature, H2O partial pressure, Ag content) needed to be tuned. Coated conductors on CSDCeO2/ABADYSZ/SS substrates achieved a high performance with a single 700 nm IJP deposition: Jc(77K)(sf) = 1.4 MA/cm2, (Ic(77K) = 98 A/cm-width). In the case of RABiT substrates high quality nanocomposite thin films were also demonstrated using a composition Y0.33Gd0.66Ba2Cu3O7 + 12% M BHO (Jc= 1.9 MA/cm2). The foreground knowledge associated to these promising performances was transferred to the industrial partners who are now in conditions to integrate the novel CSD processes in their corresponding manufacturing units.
In conclusion, the CSD approach to nanostructured superconducting thin films and coated conductor made worldwide pioneering advances strongly promoted by the multidisciplinary collaborations established within the scope of the EUROTAPES project.
3. MANUFACTURING AT THE INDUSTRIAL SCALE OF "ALL CHEMICAL" COATED CONDUCTORS WITH HIGH PERFORMANCE
Establishing good practices for industrial plants design and construction for coated conductor production based on an “all chemical” manufacturing approach has been a breakthrough of the EUROTAPES project. Two different companies have reached novel pilot lines for Chemical Solution Deposition (CSD) of buffer layers and HTS layers: Deutsche Nanoschicht GmbH (DNANO) and Oxolutia (OXO). DNANO has adopted a CC architecture based on RABiT substrates (CeO2/La2Zr2O7/NiW) while OXO uses the ABAD substrate produced by Bruker (Ce(1-x)ZrxO2/YSZ/SS). Both reel-to-reel (R2R) pilot lines have in common the use of the low Fluorine metalorganic precursors for YBCO films, however, the exact composition of the inks is different owing to the fact that the deposition system differs in both cases, as it’s described below.
OXO has designed and built two different pilot plants for R2R inkjet printing (IJP) deposition of thin films and put them in operation. The deposition system can feature at maximum speeds of 100 m/h, with tape widths of 30 mm using 512-nozzle piezoelectric printheads. The modular nature of the pilot plant allows for versatile, fast changes in inkjet conditions and drying or low temperature thermal treatments for the pyrolysis process. In 2017, an improved second pilot plant will be operative with more precise control of tape movement, enhanced resolution in droplet visualization and light-irradiation treatments A total number of 6 unit operations were included in the pilot line.
The pilot line was successfully used for inkjet printing the 20-nm thick ceria cap layer from special inks on ABAD-YSZ substrates from BRUKER. A high speed of 30 m/h makes the process competitive, taking also into account that it is made at atmospheric pressure, no vacuum is required. See figure 1.
Concerning the YBCO layer, inkjet printing was shown to be useful for obtaining superconductor films as thick as 1 micron by successive inkjet multideposition. For that goal, special inks were developed, which allows compatibility with industrial piezoelectric printheads and steady droplet injection. The deposition system being used can be still adapted to the new inks developed by ICMAB for IJP allowing to minimize the number of layer deposition and to prepare nanocomposite films. The deposited layers can be decomposed in the same R2R line. This pilot plant R2R system has also been used for deposition of CSD planarization layers in ABAD substrates, as described in Highlight No. 6, where lengths up to 10 m were produced. The ejection and size of the droplets can be monitored via a special docking position of the printhead assembly. See figure 2.
In another separate pilot plant, R2R growth of the YBCO pyrolyzed layers coming from the inkjet printing pilot line is carried out. Such plant is composed of air-tight feed and take-up chambers, a 3-meter long furnace and gas circuits. Special inserts allow for the correct conversion of 10-meters long YBCO superconducting tapes. A special design will soon allow for extending the growth to the 100 meters range. Apart from that, low pressure can be implemented up to 50 mbar. The whole system is controlled automatically through a Labview-interfaced SCADA system.
Moreover, quality control by optical microscopy and optical reflectometry with a 3 mm2 spot size and acquisition time of seconds, was shown to cope with industrial production of the chemical layers, except that of grown YBCO layer. See figure 3.
On 2016 the expanded pilot line of DNANO was inaugurated. It has started to manufacture all chemical solution coated (CSD) conductors on RABiT metallic substrates on regular basis in around 20 different devices for the several production steps all running in reel-to-reel processes. This includes all the steps of assembling the technical wire like substrate pretreatments, buffer film production, HTS layers as well as CSD silver contact layers, slitting to customized widths, and electrical and mechanical protection layers manufacturing which can be selected from electroplating with copper and lamination with metal foils depending on the target application. This new production line production enables DNANO to provide superconducting tapes in reliable high quality.
The plant increased the production capacity within DNANO by a factor of 50, but it is not running yet on 24/7 basis as an exclusive production facility as further technical adjustments to different applications as well as optimization in cost effective production methods is still ongoing in parallel to prototype production. Technical coated conductors in widths of 4-10 mm with customized shunts can be produced in typical length up to 100 m. Exceptional tape lengths up to 400 m can be produced. Wider tapes will be available in the future. Full inductive measurements of the whole length for 10 mm wide tapes as well as complete resistive measurements in 1.5 m steps can be provided.
Besides the offline control by X-ray diffraction (XRD) of the film texture by electron backscatter diffraction (EBSD) as well as precise control of physical and chemical properties of the precursor ink (like metal ion concentrations, rheology, and refraction index), the online drop watch-system can be a powerful tool to detect ink jet printing related variations of the film quality and homogeneity. Drop watch systems to control the constant ink release onto the tapes were considered to be important when the project plan was compiled. Experiments with drop watch systems from UCAM at DNANO showed that this successfully detects deviations from desired ink release, e.g. deviations in release direction at partially blocked nozzles as well as the total failure in case of completely blocked nozzles. But even when errors are detected in a very early state, this provides no appropriate solution to reset the printer by unblocking the nozzles without interrupting the printing process. However, any unblocking of the nozzles requires an interruption of the printing process for disassembling or at least cleaning and rinsing of the printhead. A more stable or self-resetting printing process was preferred. The slot-die process is much less susceptible to errors in printing related film homogeneity and it was used all during the last 3 years in D-NANO.
The permanent control of the oxygen partial pressure in the furnace exhaust gas during the crystallization annealing turned out more effective, because a (still manual triggered) feedback control loop on this parameter can be operated without stopping the running process and the relevant times for changes in the inlet gas composition or amount are in the range of several 10 minutes.
During the tape assembling process, starting from the first oxygen annealing after the YBCO crystallization, the critical current is detected via the so called Tapestar device from THEVA in a R2R process. However, the most significant quality control tool is the final R2R transport critical current measurements when a technical tape is finally fully assembled.
4. DECIPHERING THE NANOSTRUCTURAL FEATURES RESPONSIBLE OF THE ENHANCED PERFORMANCE OF NANOCOMPOSITE FILMS PREPARED BY CHEMICAL AND PHYSICAL DEPOSITION METHODOLOGIES AT DIFFERENT MAGNETIC FIELDS AND TEMPERATURES
Creating nanocomposite superconducting films and coated conductors with high performance was a key objective of the EUROTAPES project. To achieve this goal requires a full understanding of the mechanisms underlying defect creation in these films and how we can control the complex nanostructure of the REBCO films derived from the two different processing methodologies used in the project: Chemical Solution Deposition (CSD) and a Physical deposition methodology (Pulsed Laser Deposition, PLD).
An extensive use of advanced nanostructural characterization techniques was an essential requirement for the success of the project. Scanning Transmission Electron Microscopy (STEM) combined with Energy Dispersive X-ray (EDX) and Electron Energy Loss Spectroscopy (EELS) chemical analyses, as well as 3D electron tomography, were tools which provided many details of the defect structure, from the micrometric to the atomic scales. The partners with strong involvement on these tasks were UA, ICMAB and IFW. Covering these different length scales is a very important issue to be able to correlate the structural features with the superconducting performances. Actually, the project focused its interest onto three different regions of the magnetic phase diagram (low, medium and high temperatures) where it’s expected that the dimensions of the defects controlling vortex pinning and percolating critical currents through a low angle grain boundary network are modified, owing to the temperature dependence of the superconducting characteristic lengths (coherence and penetration lengths). Therefore, deciphering the nanostructure features responsible of enhancing the superconducting properties is a complex objective requiring a systematic correlation of STEM and physical properties measurements onto the same samples. Advanced measurements of physical properties were investigated by TUW, ICMAB, IFW, ENEA, UCAM and KIT.
There exist an essential difference in the growth mechanism of REBCO nanocomposites of CSD and PLD causing a completely different final nanostructure. CSD is an ex-situ growth technique where the epitaxial YBCO film grows after the secondary phase nanoparticles have been formed, both in the case of complex solutions where the nanoparticles are spontaneously segregated and in the case of preformed nanoparticles. In the case of PLD nanocomposites growth of YBCO and secondary phases occur simultaneously through evaporation of all the atomic species and this is an essential ingredient to achieve self-assembly of nanoobjects (nanorods for instance). This essential difference among both approaches lead to a separate analysis of the corresponding nanostructures.
In the case of CSD nanocomposite films the most relevant feature is the analysis of the crystal structure, size, shape, distribution, crystalline orientation and interfacial quality of the secondary phase nanoparticles. A systematic analysis of these features in spontaneously segregated nanoparticles (BaZrO3, BaYTa2O6) and preformed nanoparticles (BaMO3, M=Zr, Hf) was carried out. For instance, STEM analyses of nanocomposites based on preformed spinel nanoparticles immediately revealed that novel double perovskites, such as YBaFe(2-x)CoxO5 or YBaCuFeO5, were formed thus indicating a strong reactivity with the YBCO precursors. In the cases of fluorite and perovskite preformed nanoparticles the final nanophases (BaMO3, M=Zr, Hf) had sizes in the 10-30 nm range and it became very useful to ascertain how they were distributed within the film to ascertain its growth mechanism. It was clear, for instance, that an excessive concentration of nanoparticles at the interface lead to a degraded epitaxy of the YBCO films. Observing sharp interfaces among a seed YBCO layer and YBCO+BZO films helped to understand the positive role of homoepitaxy at high nanoparticle concentration. From the observation of the final size and distribution it was concluded that non-reactive particles display little coarsening and they can avoid agglomeration at least up to 20 % M. Another very important feature, fully analyzed by STEM, was the influence of nanoparticle features and processing steps on the induced defects within the YBCO matrix, particularly the YBa2Cu4O8 (Y248) intergrowths. These intergrowths are responsible of the increased nanostrain determined by X-ray diffraction, mainly due to the partial dislocations surrounding them, and so their final length was found to correlate with high temperature vortex pinning efficiency (strong and isotropic pinning) in the nanocomposite films. Several important parameters were found to correlate with the intergrowth density and length: orientation randomness of the nanoparticles, size and density of the nanoparticles and also kinetic features of the YBCO growth process (heating rate for instance). The observed features and the derived conclusions were essentially valid for both preformed and spontaneously derived nanoparticles, even if in the first case a smaller size and a higher concentration can be achieved.
An additional feature discovered in the scope of the EUROTAPES project was the atomic scale structure of what it was believed to be Y248 intergrowths. These defects were early detected in YBCO films and they were associated to a novel interlayer structure of the high temperature superconductors. In the YBCO nanocomposite films a very density of such intergrowths was very often observed which lead to what it was conceived as a “stoichiometry catastrophe”, i.e. the local structure was extremely different of the expected Y123 structure. The reality is that STEM combined with DFT calculations and XMCD synchrotron analyses showed that there exists a high concentration of Cu-O clustered vacancies in the double chain of the expected Y248 structure which then recovers the initial Y123 stoichiometry. These defects were shown to have ferromagnetic order and considering that their dimension is below aprox.1 nm, they are expected to influence the low temperature (T< 20 K) vortex pinning efficiency (weak and isotropic pinning). The relevance of intergrowths in the twin boundary structure of nanocomposite films was also determined and correlated with the strong anisotropic vortex pinning contribution close to the Irreversibility Line in these films. In conclusion, CSD nanocomposite films display a very complex nanostructure and EUROTAPES deeply contributed to advance in our understanding of its correlation with processing features and physical properties.
In the case of PLD films mainly BaHfO3 (BHO) and Ba2YNb0.5Ta0.5O6 (BYNTO) inclusions inside the YBCO matrix were studied. A high density of c-axis oriented BYNTO columns with a mean diameter of about 10 nm evenly distributed in the YBCO matrix was grown on single-crystal substrates at low growth rates. These structures lead to extremely high pinning forces and distinct features in critical current anisotropy Jc(Ɵ). Furthermore, we were able to adjust the orientation and distribution of BHO or BYNTO nanoparticles in thick YBCO films grown on technical templates. BHO grows typically in fan-shaped manner, increasing the pinning in broad range around H||c and flattening the Jc-anisotropy. Increased growth rates and substrate temperature lead to straighter alignment of segmented columns and the formation of ab-parallel BHO/Y2O3 platelets and Y248 intergrowths. BYNTO doped films show a mixed-type structure of shorter BYNTO columns parallel c and BYNTO/Y2O3 platelets in ab-direction having a higher thickness with increasing substrate temperature. Both kinds of platelets enhance pinning for H||ab. Finally, BHO doped YBCO films were grown on miscut single-crystalline substrates with vicinal angles Ɵ up to 40°. It was found that the growth mode switches from c-axis-oriented BHO nanocolumns (Ɵ = 0°) via a mixed distribution of c- and ab-aligned features (Ɵ = 2-10°) to purely ab-parallel BHO/Y2O3 platelets. These platelets adopt the vicinal angle of the substrate and act current blocking, increasing the anisotropy of the critical current in longitudinal and perpendicular direction.
Finally, we should also mention that STEM analysis (together with FIB sample preparation tools) of many coated conductors (ABAD and RABiT substrates) processed by CSD or PLD under different conditions at the industrial scale were very useful to ascertain the influence of specific manufacturing parameters on the micro and macroscopic defect structure development which may degrade the percolating critical currents. This includes grain boundaries, large precipitates, voids, misoriented grains, etc. and the local structure analysis could be very efficiently correlated with macroscopic physical properties characterization (transport and inductive measurements, Hall effect imaging). In conclusion, the extensive effort made in EUROTAPES in correlating local structure to physical properties and processing was a critical issue to the success of the project in developing high performance materials.
5. HIGH GROWTH RATE APPROACHES TO TUNED SELF-ASSEMBLED NANOCOMPOSITE STRUCTURES IN THICK FILMS BY PULSED LASED DEPOSITION
The analysis of the mechanisms to generate nanostructured CCs to enhance vortex pinning in PLD-grown YBCO thin film was widely investigated by several partners (IFW, ENEA, UCAM) within the EUROTAPES consortium, by combining different processing conditions, metallic substrates and compositions. The main issue in PLD grown nanocomposites is to define the composition of the secondary phase to be used (usually non-superconducting perovskites or double perovskites) and how these secondary phases self-assemble within the YBCO matrix. The main nanostructures usually observed are columnar nanorods (diameters in the range of ~5 nm) which may display a certain degree of splay, nanoplates and induced planar defects (Y248 stacking faults). After an initial screening of the most promising secondary phases, the consortium decided to center its effort in understanding the mechanisms to form nanorods based on BaHfO3 (BHO) and Ba2YNb0.5Ta0.5O6 (BYNTO). The YBCO nanocomposites based on these phases were grown first on single crystals and later on ABAD-YSZ and RABiT Ni-W substrates. The influence of films thickness and growth rates on the nanostructure was determined in conventional PLD growth. Also, novel processing approaches based on the formation of intermediate liquids during growth were investigated to further enhance the YBCO film growth rate.
IFW particularly studied the growth of undoped, BHO doped and BYNTO doped YBCO films with a thickness of up to 8 µm on industrially prepared metallic templates, such as buffered RABiT Ni-W substrates (from DNANO) or ABAD-YSZ based substrates (from BRUKER) using PLD with growth rates of up to 4 nm/s. In general, BHO/BYNTO additions to the YBCO matrix result in an elongated c-axis length and a densified YBCO microstructure by refining Y2O3 inclusions. Whereas a decrease of Jc is observed in undoped films with thicknesses above 2 µm due to misoriented YBCO grains originating from defects, as for example large Y2O3 particles. Such misoriented regions are found mainly in films with thicknesses higher than 5 µm in doped films. Both dopants act as strong artificial pinning centers and increase the pinning force density FP and irreversibility field Hirr. It was found that a higher growth rate leads to a transition in the microstructure of BHO-doped YBCO films, switching from long c-axis oriented nanorods to a more complex structure with short nanorods and ab-oriented platelets. This results in a change of the Jc anisotropy, from a large c-axis aligned pinning contribution to a more isotropic Jc(B,Θ) dependence.
ENEA focused on the PLD deposition of YBCO with BYNTO as c-axis oriented nanocolumnar inclusions on CeO2/YSZ/SS ABAD metallic templates from Bruker. The proper BYNTO columnar growth was achieved through a multilayer approach, using a seed layer of pure YBCO at the interface between YBCO-BYNTO and the ABAD substrate. The YBCO seed layer was introduced for the passivation of the CeO2 layer, having a high surface roughness (~5 nm – AFM analysis), and for roughness mitigation. TEM investigations carried out by UA clearly indicate the development of columnar BYNTO system embedded into the YBCO matrix. Thin YBCO-BYNTO nanocomposite films were deposited on YBCO seed layers with small thicknesses (~7 - 60 nm). In particular, YBCO-BYNTO films grown over YBCO seed layers showed an evident correlated contribution in the angular behaviour of the critical current density. This contribution due to the columnar growth of BYNTO in the YBCO matrix is active in the low-to-mid magnetic field range (0.5 – 3) T and evident in the temperature range (50 – 77) K. At the same time, the in-field study of transport properties in the configuration with the magnetic field applied parallel to the YBCO c-axis revealed very good low temperature behaviour with pinning force densities close to 500 GN/m3 at 12 T and 10 K.
BRUKER focused on the optimization of obtaining YSZ-ABAD CCs with the highest pinning force at low temperatures (4.2 K) and ultrahigh magnetic fields (> 18 T). They were able to generate a novel nanostructure combining BZO nanorods with a fan-shaped distribution and pressure triggered stoichiometric variations. Strain maps obtained through STEM investigations by UA showed that the nanorods generate a dense nanostrain within the YBCO matrix. This advanced nanostructure demonstrated to lead to the highest critical currents achieved so far under these conditions (Ic(4.2K,18T)= 1250 A/cm-w for 22 m), even in long length conductors (Ic(4.2K,18T)= 1000 A/cm-w or Ic(4.2K,5T)>2500 A/cm-w for 600 m).
Finally, UCAM focused on controlling the growth of the YBCO matrix with 5 mol% BYNO nano-inclusions at very high growth rates with the goal of having high in-field critical current Jc(B,Θ) at low cost. At low YBCO PLD growth rate (~1 nm/s), an immiscible secondary phase (BYNO) tends to be well self-assembled into (vertical) nanorods, (horizontal) nanoplates and/or nanoparticles coherent with the matrix, contributing accordingly to an increased Jc(B,Θ) through the flux pinning effect in the relevant directions. At higher growth rates, surface diffusion, of the ablated and deposited PLD material, becomes the limiting factor for the good YBCO epitaxy and BYNO self-assembly. Building-up on earlier knowledge of liquid assisted growth, UCAM developed an in-situ process of Liquid-in epitaxial (LiE) growth. In this case the growing YBCO with BYNO has small amount liquid phase component (Y-BaO-CuO) added during the deposition and "consumed" during the growth. As a result, on (100) SrTiO3 substrates, at very growth rates (>15 nm/s, i.e. ~1 µm/minute), an extraordinary increase in Jc(B,Θ) has been obtained, compared to standard PLD growth. Invoking different growth modes of the self-assembled BYNO, tuning of the Jc(B,Θ) has been achieved by modifying growth temperature, hence having Jc anisotropy from c-axis aligned pinning contribution to more isotropic Jc(B,Θ). Similarly, on YSZ-ABAD metallic substrates (from Bruker), Jc(B,Θ) in LiE films were comparable to the results for usual PLD films grown at 10 times slower rate. Jc(B,Θ) was not thickness dependent for films as thick as 2 μm, indicating there is no thickness limit to be expected.
In conclusion, PLD growth of YBCO nanocomposites was very widely investigated within the EUROTAPES project using the metallic substrates generated by the industrial partners and a large body of knowledge was generated allowing to optimize the superconducting properties at different temperatures and magnetic fields.
6. MANUFACTURING AT THE INDUSTRIAL SCALE OF HIGH PERFORMANCE COATED CONDUCTORS BASED ON ABAD SUBSTRATES IN THE ISD APPROACH
Full manufacturing plant was established to enable an industrial scale manufacturing of >600m long HTS coated conductor by BRUKER based on YSZ-ABAD substrates. The main innovative idea for the HTS film deposition is based on a double disordering (DD) mechanism of YBCO nano-structure where (i) an intrinsic disorder is caused by periodic modulation of oxygen pressure during high-rate pulsed laser deposition (HR-PLD), and (ii) an extrinsic disorder is activated via injection of nanoparticles of a foreign material added to the composition of the ablated target.
Double-disordered YBCO layer has been shown to display the highest critical currents in magnetic field (Ic>2500 A cm w at 5 T, perpendicular field at 4.2K).
An up-scaled (>600m length) HR-PLD machine was developed and employed for tape manufacturing of CCs with nanostructured HTS layers. See figure 4: PLD up-scaling: PLD 600. See figure 5: View of drum with helical winding: 610 m long tape after deposition of HTS layer.
Corresponding processing stations of the plant at BRU included tape polishing, planarization (OXO), ABAD buffering, HR-PLD for DD-YBCO processing, as well as metallization of the tape via deposition of silver protection layer and further galvanic plating with copper.
The main manufacturing steps were adjusted to the throughput of 40 m/h and a continuous production cycle of >48 hours.
Very important initial steps of tape processing are long tape polishing and quality control via automatic imaging of tape surface. Surface quality determines homogeneity of critical current within the long length tapes. Sufficient surface quality can be provided by planarization of the substrate via an additional oxide amorphous layer achieved by solution deposition planarization (SDP).
The idea of planarization layers on metallic rough substrates produced by reel-to-reel inkjet printing was successfully demonstrated up to a length of 100 meters and speeds close to 40 m/h by OXO. In short samples, inkjet-planarized rough unpolished stainless steel substrates rendered an Ic of 50% that of fully polished stainless steel. This indicates the huge potential for cost reduction in coated conductors with ABAD-architectures since the time-consuming and costly polishing step is avoided by the deposited layer from inks at high speeds.
Planarization oxide layers between the metallic substrate and ABAD-textured YSZ layer were manufactured in industrially-meaningful lengths (100 meters). OXO and ICMAB closely collaborated with BRUKER towards the definition and realization of high-performing cost-effective coated conductors in long lengths.
In addition, epitaxial flat ceria buffer layers were also deposited on ABAD-textured YSZ in the reel-to-reel inkjet printing pilot line at OXO at speeds as high as 30 m/h and maximum lengths of 10 meters. This approach might also be an industrial possibility to integrate in the manufacture of coated conductors in terms of better control of the morphology of the buffer layer. ICMAB had also an important involvement in the task.
For >600m tape lengths, as a temporary technical solution, a physical vapor deposition of alumina-YSZ combined layers was used by BRU before the SDP technology of planarization is up-scaled to the 600m lengths.
An upscaling of technological equipment at Bruker was performed together with the implementation of Quality control tools and finally Quality Control System and other “tools” developed within the EUROTAPEs project. One of the outstanding features here is implementation of an Ultra-High-Speed PLD that leads to a substantial benefit in feasibility of tape production.
As a result, 609 m long tapes manufactured via proof-on technology for ABAD based architecture meet the main project requirements. These are the longest CCs in Europe fabricated so far; the critical currents in high field are at the champion level worldwide (data of FHMFL, Tallahassee). See figure 6: Process up-scaling (architecture 1, end pieces of 602-609 m long tapes). Recent measurements at Tallahassee, Jan 24, 2017, D. Abraimov, D. Larbalestier width of the tape corresponds to 4 mm.
Cost assessments performed also for different tape applications result in rather optimistic numbers, well acceptable for various technical fields.
At the beginning of the Eurotapes project THEVA finished assembling its fully automated pilot line based on the Inclined Substrate Deposition (ISD) approach and started the regular production of CCs. The tape length was 60 m. After stabilizing a good production yield for a sufficiently high performance class (Ic~300 A/cm-width), THEVA started a development program to increase the tape length to 600 m. The goal was to:
• increase process speed,
• improve material efficiency,
• improve reliability of the machine components and reduce demand for maintenance,
• improve film quality by optimizing deposition parameters.
THEVA uses an all electron beam evaporation approach, meaning that all individual layers of the coated conductor are deposited by electron beam evaporation. This allows focusing the development on only a few major components. The results can then be applied to all processes and production machines. To ensure high yield and constantly good quality over the whole tape length of 600 m, all components must not fail over a process time of at least 20 h. Also, all process parameters need to be constant over the same time.
In 2016, THEVA introduced three-shift operation to its production to cover the long deposition times and additional maintenance work. With the first improvements in place the tape length to be processed was increased to 350 m. Tape performance and yield was maintained at the same level as with 60 m process lengths. In the first quarter of 2017, the tape length was increased to 600 m in the superconductor process and to 1200 m in the buffer layer processes. For this the tape speed in most fabrication processes was enhanced by at least 50%. This major step required significant changes especially to the evaporation system. E.g. the e-gun emitter design was improved to reduce wear and ensure long operation times. Also, the evaporation system was altered to increase material efficiency by 60%. The design of almost all vacuum components was revised to eliminate time-consuming maintenance.
To stabilize process parameters, the level of automation of the pilot line was enhanced. Deposition rate is now controlled automatically to keep a constant film thickness. Additionally, new sensors to measure tape temperature and thickness of metal layers were developed to have better control over these quantities. Last but not least, THEVA was closely working together with its suppliers to improve the quality of the raw materials. This and further optimizations to all processes now make it possible to reach tape performances of 500 A at 77 K in self field in 12mm wide tapes with a production length of 600 m.
7. ROUND WIRE PRODUCTION METHODOLOGY BASED ON COATED CONDUCTORS (CONDUCTOR ON ROUND TUBE, CORT)
In the Coated Conductors (CCs) based on the high-temperature superconducting material REBCO a metallic substrate tape (stainless steel, Hastelloy, NiW alloy) is covered by a thin layer of REBCO and eventually it’s finally covered by protective metallic layers (silver, copper). Therefore the CCs tapes have a form that is rather different from the round or oval wires and cables made from normal metals or low-temperature superconductors. Production of round wires from CC tapes would be a break-through in the CC application in various areas of electric power engineering because the technology already developed for low-temperature superconductors could be used directly or after minor modifications.
Attempts to deposit a superconducting layer directly on a round substrate did not lead to conductors of sufficient transport capacity. Therefore in the EUROTAPES project we have developed the concept of round wires made of CC tapes helically wound with the lay angle Ɵ on a round core with diameter Df. See figure 7.
During the project execution the alternative of using a metallic tube as the central core emerged as the most promising because of several advantages. Copper tube of ~1 mm wall thickness is on one side tough enough to offer necessary mechanical support for the tapes but on the other hand it is flexible enough to allow winding of coils with the diameter as small as 100 mm. Moreover such arrangement for which we started to use the abbreviation CORT (Conductor-in-Round-Tube) provides the possibility to use the central tube as a channel for the flow of coolant that could be e.g. liquid nitrogen or gaseous helium. We have also verified that an insulation from polymeric foam could arrange for sufficient thermal insulation of a single wire used for current transport. In case of coil a collective covering of all the winding turns the coil would become lightweight and compact.
Application of CC tape for the production of CORT round wire requires to test first the tape properties in order to identify the critical parameters limiting the geometry of tape arrangement in the wire. In particular the deformation of tapes by wrapping around round core leads to certain reduction of critical current at too small diameters. At IEE the rig for in-situ testing of critical current degradation at tape wrapping has been developed and 4 mm wide tapes from two commercial manufacturers (Superpower, Sunam) as well as from two project partners (DNANO, THEVA) investigated in liquid nitrogen bath. Wire diameter of 5 mm can be achieved in this kind of wire architecture.
Important parameter in the wire manufacturing is the pulling force exerted on individual tapes. With this force the flat tape is deformed to follow the cylindrical surface that for the first layer is a smooth round core. However in the successive layers the tapes are forced to accommodate to the outer surface of previous layer of tapes that commonly contains gaps between tapes and also sharp tape edges. For each of the tapes used for CORT manufacturing first a short (0.5-1 m) model was prepared by hand, using the procedure that keeps constant the selected pulling force. Testing of such models in liquid nitrogen revealed that CC tapes of various architectures and prepared by different technological procedures require rather different pulling forces in order to achieve a regular lay-out of the wire without substantial degradation of its critical current.
CORT round wire with the length exceeding 100 meters can be manufactured using the machine that was developed during the project. Currently it contains two carousels, each accommodating 4 CC tapes on supply spools. Set of guiding wheels leads the tapes under desired angle and with the preset pulling force on the central core that is moving with the speed controlled by an independent drive. Each of the two carousels is rotating by the action of its own drive. The total of 3 drives is controlled by the software that secures perfect coordination of movements during all the steps of CORT winding. Photo of the machine follows: See figure 8.
This machine was utilized to produce several samples of CORT round wires from tapes delivered by the project partners. The picture showing the test in liquid nitrogen bath of the 3 meters long round wire made from 8 tapes is below: See figure 9.
The advance in mass production of 4 mm class tapes by European tape producers (THEVA and DNANO are our partners in this activity) is a pre-condition for further progress towards a complete wire with all the necessary accessories (envelope, terminations, sensors,...).
8. CONTINOUS EX-SITU QUALITY CONTROL SYSTEM BASED ON HALL EFFECT MAGNETOMETRY
The critical current is the final figure of merit of a coated conductor. It is hence mandatory to ensure a nominal value along its entire length as a final quality control. Although different applications are operating at different fields and temperatures and the critical current is important for them only under these conditions, the assessment of the critical current at liquid nitrogen temperature and low fields is often sufficient for quality control since deviations from the standard performance due to irregularities during production harm the critical currents at all fields and temperatures. There are two common methods for measurements of the critical current in long length conductors. Firstly, a direct injection of an increasing current on a short segment (typically one meter) of the tape until a voltage is detected. This method directly probes the critical current without any modelling. However, the application of the needed (large) currents is demanding and the spatial resolution is low, essentially given by the length of the tested segment, which cannot be made arbitrarily short because a tradeoff between measurement time and spatial resolution has to be made. For these disadvantages, a magnetic assessment of the critical current is made instead in most cases. THEVA is offering a commercial system for this purpose, called TapeStar, which is in use at nearly all commercial producers and many research institutions. The currents are not applied by an external source in this device, but induced by a local magnetic field. These currents in turn generate a magnetic field, which is recorded by a linear array of Hall probes. The obtained field profile is then compared with the ideal one to estimate the critical current. The method is well suited for the identification of defects along the length of the conductor, quantitative predictions of the local critical current on the other hand need a calibration with resistive measurements of a reference tape and fail if the field profile deviates strongly from the ideal one.
A new evaluation algorithm for measurements performed by THEVA’s TapeStar was developed by TUW with the aim of improving the quantitative prediction of the critical current and, even more important, get full benefit of the high spatial resolution of these measurements. The linear Hall array offers the possibility to assess variations of the critical current not only along the tape with a resolution in the millimeter range, but also the distribution of the current density across the width of the tape. This information is very valuable for the identification of problems during the tape production and for predicting the performance of the conductor after slicing to tapes of smaller width or filamentization. Although the measured data contain local information of the magnetic field the underlying current density is not unique, because of the non-locality of the problem. The field profile is recorded only along one line, but the currents flowing in the vicinity of this line are contributing to the field at the positions of the Hall probes as well; thus, in a first step, the geometry of the induced current loops had to be determined to separate the local information.
It turned out that the calculated local current depends significantly on the chosen mesh for the discretization of the current density within the tape. This made the solution unstable against variations of the tape position with respect to the Hall sensors as well as changes of the effective width of the superconducting layer, which is not necessarily the same as the geometric width of the tape and may even change along the tape. An adaptive local mesh was introduced to solve this issue and provides, as a side effect, an estimate of the error of the derived current density. One example of the derived critical current densities is shown in the figure.
See figure 10: Test measurement of a short piece of coated conductor. The absolute value of the critical current density is shown in the uppermost panel, its components parallel and perpendicular to the tape are displayed in the panels below. The bottom panel contains the error estimation.
Improvements of the Tapestar sensor system were developed in order to get a good quality of the measurement. For example, the distance between the sensors was minimized to improve the resolution and the horizontal position of the sensors was controlled with maximum accuracy.
The new evaluation algorithm together with the optimized sensor system can now be implemented in an improved version of the Tapestar System. This would then give unsurpassed data quality for R&D as well as routine quality inspection of HTS wires in a production plant.
9. NEW METALLIC SUBSTRATE COMPOSITIONS BASED ON NIW AND CU ALLOYS
The development of novel Cu substrates where the poor mechanical properties of RABiTTM Cu substrates are overcome as well as qualifying new highly textured, non-magnetic NiW substrates with a tungsten content around 9% are outstanding objectives of EUROTAPES.
For Substrates based on Cu-alloys solution hardening was the method of choice for the production of a more economic metallic substrate with reduced magnetism with respect to the currently available Ni-5at%W substrate. LFL and ENEA showed that the most promising candidate to be alloyed with copper with suitable cube texture was germanium, while nickel was improving mechanical properties. The composition achieved with excellent texture and slightly improved mechanical properties was CuNi10%Ge0,8%.
The binary alloy Cu 50% Ni 50% develops a very sharp cube texture and can be used as parent alloy for the development of ternary alloys.
In this aspect, a set of Cu-alloys (CuNiX) with 49,5wt% Cu, 49,5wt% Ni and 1w% of the alloying element of choice (Ge, Mo, Fe, Nb, Ta) were prepared to improve mechanical properties to the extent possible.
The tapes were obtained by cold rolling (deformation degree 98%) of the arc melted and homogenized (12 h, 800°C, atmosphere Ar/5%H2) starting alloy. After a two stage rolling (TSR) and two-step annealing (TSA) process the final texture was obtained. Using this novel process route a cube texture of >97% (tolerance angle 12%) was achieved for alloys with Nb.
Ternary CuNiNb alloy presents enhanced mechanical properties and have in the case of CuNiNb a yield strength of 135 MPa which is close to the requirement of 150MPa.
The qualification of the production process and enhancing the magnetic properties towards non-magnetic NiW substrates was an essential objective of the EUROTAPES project handled by EVICO.
Based on the technology developed at IFW 80 µm thick Ni7.5at%W and Ni9.0at%W metallic substrates up to lengths of 100 m were successfully manufactured. The main focus of the work was on optimization of the reel-to-reel (RTR) - production and annealing process to enable future industrial production. Optimized RTR texture annealing conditions resulted in reproducible high cube texture fractions of higher than 99 % for Ni7.5at%W and higher than 97 % for Ni9.0at%W representing very good results. This is a great progress in RTR-substrate processing, especially as with increasing W content the formation of grain boundary grooves is increased, the production process technology becomes more complex and process windows become very narrow.
The whole manufacturing process has been optimized regarding cost. As a result, the furnace temperature during the heat treatment could be lowered and the process time could be reduced by 30 min for a 100 m Ni9.0at5W tape by maintaining the same high texture quality of the tape. For an assumed demand of 100 km tape per year the reduced process time sums up to 500 h. These new production process parameters allow reducing cost by saving time and energy and leading to a higher efficiency of the process enabling an increase of production capacity.
In conclusion, the new Cu approach to substrate material for coated conductors made recognizable progress. The successfully manufactured non-magnetic Ni9.0at%W tapes with a length of 100 m were used for the production of a fully superconducting tape within the collaborations of the EUROTAPES project.
10. ENVIRONMENTAL ASSESSMENT OF SUPERCONDUCTING TAPES AND ROUND WIRE CONDUCTORS BY USING LIFE CYCLE ASSESSMENT (LCA) METHODOLOGY
In the framework of EUROTAPES project it was realised an environmental analysis of the different superconductor architectures developed and eligible to be scale-up at industrial scale. The main objective of this analysis was to calculate the potential environmental impacts associated to the production stage of these superconductor architectures. The environmental impacts of different production substages and processes involved were assessed, and main hotspots were identified. Besides this, alternative compositions, technologies, processes and methods developed within EUROTAPES project were evaluated and were compared with the current ones (or conventional), in order to determine the most environmentally friendly options and make final recommendations to reduce the environmental impact of superconducting architectures produced.
The methodology used to perform the environmental analysis was the Life Cycle Assessment (LCA) methodology. The scope of the analysis was defined as cradle-to-gate; that it means that for each architecture analysed, all the environmental impacts linked to the production stage were calculated, including the upstream processes (extraction and transformation of raw materials and production of energy used). Life cycle stages beyond the production of the final superconductors (transport, use and end-of-life) were excluded since they are out of the scope of the project and there is no available information. All the data used to calculate the environmental impacts of superconducting architectures was provided by project partners. When data was not available, data from literature or databases (GaBi and Ecoinvent) was used. All this data was introduced to LCA software (GaBi abd SimaPro) in order to calculate the environmental impact contributions of superconducting architectures on eight environmental impact categories: acidification, climate change, freshwater eutrophication, human toxicity, ozone depletion, photochemical ozone formation, water resource depletion, and mineral, fossil and renewable resource depletion.
Three different superconducting architectures were assessed:
1. Low cost superconducting tapes: NiW RABIT substrates architecture.
2. Medium cost superconducting tapes: SS substrate/ABAD-YSZ architectures.
3. Round wire conductors based on low cost superconducting tapes (hastelloy substrate architecture).
The results of the analysis on low cost superconducting tapes (NiW RABIT substrates) revealed that final protective coatings applied (silver coating and copper electroplating) have the highest environmental impact contributions, to the overall architecture. These environmental impacts are related to the extracting and obtaining processes of the raw materials used in the coating processes (copper oxide and silver) and also to the energy consumed during the copper electroplating process. The manufacturing of buffer and YBCO layers have high environmental impact contributions affecting the climate change and the ozone layer depletion, as a consequence of the energy consumed, solvents and precursors employed in the manufacturing processes of both layers.
In regards to medium cost superconducting tapes, two different production approaches (or routes) were assessed: the Pulsed Laser Deposition (PLD) route and the CSD (Chemical Solid Deposition) route. For the PLD route, the majority of environmental impacts are associated with the electrochemical polishing process, due to their high energy requirements, as well as to the final protective coatings, due to the raw materials used (as it has explained before). Concerning the CSD route, once again, final protective coatings (silver coating and copper electroplating) cause the main environmental impacts to the overall architecture. In addition to this, YBCO layer preparation contributes also with high environmental impacts in the ozone depletion as a consequence of the YBCO fluorinated precursors used.
Finally, the environmental analysis performed on round wire conductors based on low cost superconducting tapes concluded that main environmental impacts are related to the hastelloy substrate manufacture, especially to the nickel employed. Moreover, round wire process cause also remarkable environmental impacts as a consequence of the electricity consumed during the process. Last, the high thermal superconducting layer (GdBCO) production has also important environmental impacts, especially on climate change and ozone depletion, because of the use of Gadolinium, a rare earth element with a complex and selective obtaining process associated, which mobilises high flows of materials and energy.
As has mentioned before, alternative compositions, technologies, processes and methods were also evaluated and compared with the currently used, in order to determine the most environmentally friendly options. Results of this analysis reveal that in general, innovative processes developed or evolved thanks to EUROTAPES project have lower environmental impact contributions in comparison with conventional or currently used processes. The main highlights and recommendations proposed are:
- Results of the analysis conducted in the RABIT architecture confirmed that high W-alloyed Ni substrate (Ni9%W) has a better environmental profile than low W-alloyed Ni substrate (Ni5%W), achieving an environmental impact reduction about 10% in the substrate manufacturing substage, for all the eight impact categories studied. Therefore, the use of high W-alloyed substrates is particularly recommended.
- The LCA applied in this project proved that the innovative SDP process is more sustainable than the electrochemical polishing process. The application of SDP represents important environmental impact savings in the substrate preparation substage (between >99% to 61%) and for the overall architecture (between 8% to 58%). So as to decrease the overall environmental impacts of medium costs superconducting tapes, the application of SDP process instead of electrochemical polishing process to prepare SS substrates is recommended.
- The new metalorganic precursor solutions with low fluorine (low-F) content for YBCO layers are more environmentally friendly than conventional TFA solutions; it has been demonstrated a reduction of the environmental impacts of YBCO layer by 67%, for the ozone layer depletion, due to the lower generation of emissions of fluorinated compound into the atmosphere.
- An increase in tape's width to 40mm could reduce the environmental impacts associated to the production of medium cost superconducting tapes from 88% to 3%, depending on the impact category selected, so it has demonstrated to be an interesting proposal to reduce the environmental impact of superconducting tapes.
- On the other hand, IJP processes have reflected evident improvements in the energy consumption in comparison with other processes studied. Moreover, the promotion of energy efficiency strategies and/or the incorporation of energy supplied from renewable energy sources were determined as interesting actions to reduce the environmental impacts of template, buffer and HTS layers for the three architectures studied.
The EUROTAPES project has made evident their contributions to the improvement of superconducting technology in Europe and their commitment to environment and society, by developing new environmentally friendly solutions for the future of superconductivity industry.
Potential Impact:
High Temperature superconductors (HTS) are now very close of spreading power applications while they have also open new frontiers in the use of superconducting magnets. Coated conductors (CCs) have emerged as the best opportunity to enable a broad penetration of HTS on all power system and magnet applications. The main challenge of EUROTAPES was to be able to implement materials with novel nanostructures and reliable processing methodologies for long length CCs manufacturing, beyond 500 m in length, with a cost/performance ratio making them attractive for a wide market penetration.
EUROTAPES has made outstanding scientific and technological advancements providing definitive progress towards approaching the goal of achieving a low cost/performance ratio of CCs. The metrics to evaluate progress in the materials development and manufacturing capabilities, as well as capability for market penetration, need to be referred to the specific working conditions of the power systems and magnets intended for final use. Three different types of final use applications have been considered for the CCs leading to different working magnetic fields (low, high and ultra-high magnetic fields) and temperatures (77 K, ~30 K and 4.2 K, respectively). The techno-economic metrics are then defined for each of these working conditions. For instance, for applications at 77 K and self-field (cables, FCL, transformers) the required cost/performance ratio is ~100€/kA m for 1 m of conductor and 1 cm wide. Instead, costs below this value can be achieved at 4.2 K under a magnetic field of 30 T (ultra-high field magnets).
The EUROTAPES project defined a twofold strategy. First, to develop novel advancements which decrease the CCs manufacturing cost. The paths to follow were: simplified conductor architectures and less costly methodologies implemented in long length manufacturing processes with a high throughput and high yield. The second goal was to enhance the superconducting performance of the CCs under the working conditions of the different applications, i.e. mainly to enhance the total critical current Ic (H, T) of the conductors under magnetic field.
The deployed research activities have boosted the European industry of superconducting materials towards a worldwide competitive position for HTS power systems and magnet development. This is reflected in many new initiatives at industrial and R&D levels in Europe where the EUROTAPES partners are involved.
The impact of HTS in achieving the EU vision of a smart and sustainable electrical grid with a high percentage of renewable sources is very high. Electrical power technologies based on HTS have a strong potential for improved efficiency in generation (wind generators) and transmission, as well as in enhancing power grid stability. Transport applications (aeronautics, ship propulsion) may also benefit of these developments. The unique properties of HTS key for these achievements are: 1/ Low losses in ac and dc power systems (cables, transformers, motors, Fault current limiters); 2/ Increased power density and simplified engineered systems, lighter and smaller equipment (generators/motors); 3/ Fast impedance transitions allowing to reach an enhanced grid stability (FCL); 4/ High energy and power densities for electromagnetic energy storage (SMES).
The impact of HTS conductors in scientific and biomedical applications requiring high magnetic fields will be as well huge. The future of large scientific installations, using accelerators (CERN) or fusion installations (ITER), will make extensive use of the unique HTS magnet capabilities. The mid-term technological strategies in these areas are closely determined by the availability of HTS conductors and cables. Finally, the large demand of superconductors for medical and biochemical applications (MRI, NMR, compact accelerators for hadron radiotherapy) will also widely benefit of making available a new series of high and ultra-high magnetic field HTS conductors.
Main dissemination activities and the exploitation of results
Dissemination activities
EUROTAPES project has had a significant impact on the scientific community thanks to its excellent results but also on the European society being its citizens that can be defined as the “public” in this case. Therefore, efforts have been made to inform the general public directly mostly through digital channels and indirectly through the media that contribute largely to a wide diffusion of the news.
The objective of the communication concentrated on the general public is to show them that superconductivity is essential for Europe for various aspects as it has a direct impact on many economic sectors (renewable energies, electricity networks, astrophysics, competitively, environment and more) and that European research is delivering excellent and concrete results.
Target audience: It includes amongst others the scientific and academic community, the industry and end users, and public administration and regulatory authorities.
Main actions of public awareness
Various actions were undertaken to ensure an effective public awareness: direct and indirect ones.
The direct ones are defined as news items published on the project’s website (or of the partners) with the objective that the public will read it directly without being digested by external persons. The advantage is that there is a full control over the content that is being published. However, the amount of views and the outreach of the news item is limited. The audience will reach the webpage either because they know the website and they want to follow the news of the project or of the organisation, or because the search engine they use will bring them to this page because the key words correspond to the news item. In any case, the outreach is limited as the EUROTAPES website has on average around 10 visits per day.
The indirect actions are the ones with the help of external persons such as journalists. The news item is being sent to journalists and according to their interest, the importance of the news item and the moment, they make a news item out of it by mixing it often with other sources. The outreach of these indirect actions is much bigger than of the direct ones although the inconvenient is that the consortium cannot control what is being published. However, this is necessary so journalists can cross information and compare facts in order to inform their readers. Nevertheless, from experience, the content published by the media was quite accurate and close to the facts. Therefore, the consortium was very glad to benefit from visibility with the help of the media.
Three main actions were done during the project to raise public awareness around the project:
a. Websites publications
On the EUROTAPES website, 36 news items were published during the lifetime of the project, which corresponds to a more than one item every two months. As said, on average, the website has around 10 visits per day since the analytics service was installed (November 2013). In total, it benefited from 19’000 visits. A peak of 202 visits in one day was reached when the press conference was organised at the end of the project (15th of March 2017).
b. Press release
On the 17th of May 2016, one year before the end of the project, the consortium issued a first press release that was distributed to various media organisations in Europe with the help of a large news agency (Business Wire). The content was elaborated by the coordinator and the communication manager with the approval of the consortium.
A total of 19’506 views has been reached according to the statistics of the news agency although the large part of these views were made during the first 24 hours after publishing the news item.
It was translated from English into German, French, Dutch, Italian and Spanish in order to better reach the media. This press release was crucial to start informing the press and the public about the existence of EUROTAPES and its impact in the scientific environment and on the economy. The impact was quite successful and it was a good preparation for the second and final press release and conference.
c. Press conference
At the very end of the project with the results clearly defined, the major event of public awareness was organised in Barcelona between the ICMAB, Oxolutia and LEITAT with the strong support of the representation of the European Commission in Barcelona and its media team from DG COMM. On the 14th of March 2017, Prof. Xavier Obradors, Prof. Teresa Puig, Dr. Albert Calleja presented EUROTAPES during a press conference (accompanied by a press release) in Barcelona in the representation of the European Commission in Barcelona. Around 15 journalists attended, 3 additional interviews for radio and TV were made and many news articles were published in international media.
A dissemination leaflet has been done and is available on the EUROTAPES website. In the leaflet, the EUROTAPES technical information have been synthesized for a better comprehension of the general public. It has been updated and distributed to all partners and all stakeholders met during the project during events, meetings and conference. An updated version has been released in the last period of the project.
Scientific Dissemination
The main objective of the Scientific Dissemination is to spread the knowledge to the Scientific Community, within EUROTAPES consortium the following activities have been performed.
99 Scientific publications
299 Dissemination activities including, Oral presentations, Poster, Workshop, participation in conferences, articles.
Exploitation of the results
Regarding the exploitation activities, in order to ensure that the R&D developments of a project have an impact, it requires not only the obvious research development but also the analysis from a market point of view, in order to map the project outcomes onto the actual market needs and realities
Eight Key Exploitable Results (KERs) have been identified and a strategy of exploitation has been proposed and it will be carried out by the partners, owners of these technologies jointly with other partners that have interest in using these results. A brief summary of the technology analysis is provided below:
The first KER (KER n°1) is the Ink Jet Printed planarization layers of metallic substrates. It is the amorphous oxide layers deposited by the Chemical Solution Deposition technique (SDP, Solution Deposition Planarization) on metallic substrates for IBAD or ABAD template deposition. This can be accomplished by inkjet printing deposition in reel-to-reel configuration at tape speeds of 40 m/h approx. The surface imperfections like scratches, pores or protuberances are covered and filled with the ink, which becomes a solid planarization layer upon suitable thermal treatments.
The second KER (KER n°2) is Metal Oxide Nanoparticles stabilized in alcoholic media. More precisely, these are Stable Alcoholic Colloidal Solutions of Metal Oxide nanoparticles prepared using the polyol synthesis by Thermal, Microwave(MW) and/or Solvothermal activation approaches. Our unified methodology offers stable mono (CeO2, ZrO2) and binary metal oxide (MFe2O4, M=Fe, Co,Mn and BaMO3, M=Ti, Zr, Hf), colloid solutions with a high size control and narrow dispersion in a broad range of concentrations (up to 0.2M) in alcoholic solvents.
The third KER (KER n°3) is called Low fluorine metal organic solutions for Ink Jet Deposition of superconducting layers. Briefly explained, this entails novel compositions of inks with metalorganic precursor solutions of Y, Ba and Cu with a strong reduction of the F content and additives and solvents which are adapted to IJP deposition of homogeneous thick films in continuous mode using piezoelectric heads.
The fourth KER (KER n°4) are conductors on round core cable. These are round wire made of HTS tapes wound helically on metallic tube and covered by polymeric foam that insulates thermally and contains a cooling channel.
The fifth KER (KER n°5) are Advanced (non-magnetic cube textured) Cu-based metallic substrates. In entails the production of nonmagnetic cube metallic substrate with recycled copper, reducing raw material cost and energy.
The sixth KER (KER n°6) is the Ink Jet Printing reel-to-reel pilot plant. Continuous production of thin films from chemical solutions has been materialized in a reel-to-reel pilot plant including ink jet printing as deposition method.
The seventh KER (KER n°7) is the Advanced Magnetoscan system for quality control of coated conductors. The measurement of the critical current of coated conductor tapes is most important for quality control and has to be done with every tape.
The eighth KER (KER n°8) are absolutely straight, non-magnetic and at the same time highly cube textured Nickel-Tungsten-based metallic substrate tapes for coated conductor production.
Taking all this into consideration, we can conclude from one side that all the channels used to disseminate the projects have achieved the expected impact and that all the consortium has contributed to it. From the other side, the project has finished with eight exploitable results that have a potential market within the superconducting sector, there is an exploitable plan set for each result individually and for EUROTAPES as a whole and the partners involved are committed to continue their exploitation activities beyond the project.
List of Websites:
http://eurotapes.eu/
Project Coordinator
Prof. Xavier OBRADORS
AGENCIA ESTATAL CONSEJO SUPERIOR DE INVESTIGACIONES CIENTIFICAS
xavier.obradors@icmab.es
European researchers and industrial companies have joined forces within EUROTAPES to make progress towards providing long length substrates for use in high current Superconducting (SC) tapes, using both vacuum deposition techniques (Pulsed Laser Deposition, PLD) and chemical (Chemical Solution Deposition, CSD) methods for the multilayer growth of coated conductors (CCs) based on REBa2Cu3O7 (RE=Y, Gd; REBCO). Development of novel nanostructuring approaches has allowed to achieve improved performance at high and ultrahigh magnetic fields while progress in manufacturing control has pushed CCs industry to make possible the power applications of superconductivity.
The overall goal was to decrease the cost/performance ratio (down to ~100 €/kA-m) of the CCs, as measured by the cost of fabricating 1 m of conductor, 1 cm wide divided by the critical current Ic at 77 K. The combination of high performance (large Ic) with a high production volume has been shown to make feasible this goal.
The concept of EUROTAPES has been to integrate the advanced materials developments into longer length CCs and to generate the process and control system know-how necessary to move into production. The best combination of the physical and chemical methods has been used with two types of substrates: Alternate Beam Assisted Deposition (ABAD)-coated stainless steel and biaxially textured Ni-W Rolling Assisted Biaxial Texturing (RABiTTM).
Two CCs architectures have be chosen for ‘a demonstration stage’: ABAD-PLD approach (lengths in excess of 600 m) and RABiT-CSD approach (CCs longer than 300 m).
Manufacturing developments, including definition of quality assurance and quality control methods, have been one of the focus of the project. Both of these thrusts have been underpinned by advanced characterization and measurements with nanostructural (Scanning Transmission Electron Microscopy) and high magnetic field transport and magnetic properties.
The CCs targets several final uses: i/ cables, transformers and fault current limiters running at high temperatures (~77K) and self-field; ii/ motors/generators, magnets and SMES (Superconductor Magnetic Energy Storage) working at high magnetic fields (3-10T) and intermediate temperatures (30-60K) and iii/ magnets for NMR, fusion, compact accelerators and High Energy Physics working at low temperature (~5K) and ultra-high magnetic fields (>20T).
The main scientific and technological advances achieved are:
• Simplified metallic substrates cost-effectively planarized by chemical methods for ABAD templates.
• New metallic non-magnetic (Ni and Cu based) substrates with reduced magnetic AC losses.
• Preparation methods of stable alcoholic solutions of well dispersed oxide nanoparticles with tuned size useful for a novel route of nanocomposite thin film growth.
• Low Fluorine content eco-friendly colloidal solutions, with preformed nanoparticles, used to grow high current nanocomposite CCs by CSD based on Ink Jet Printing.
• Development of processes to prepare engineered nanocomposite CCs using CSD or PLD with very high pinning forces and Ic at high and ultrahigh magnetic fields based on thorough knowledge on the relationship among nanoscale defects and vortex pinning. A worldwide record performance in long length CCs working at 4.2 K and 18 T has been achieved.
• A new round wire conductor architecture (CORT, Conductor-in-Round-Tube) which can be adapted to design compact cables with improved transport capability.
• Improved high throughput processing methodologies with high yields and performance and the cost / performance metric required for market penetration, including implementation of in-situ and ex-situ continuous quality control tools based on optical and Hall mapping of CCs for the fabrication and testing.
• The convincing demonstration of the scalability of coated conductor manufacturing by Bruker through long length production of ABAD CC (+600 m) based on proven advances in materials and PLD processes.
Project Context and Objectives:
The project has focused in developing new routes towards CCs with enhanced performance, higher robustness, simplified conductor architectures and more environmentally friendly chemical processes and quality control tools for enhanced throughput on manufacturing. The overall goal has been to decrease the cost/performance ratio.
The first issue handled by the project was the development of novel features of two conductor architectures: the ABAD and RABiT approaches. In the first case, the main achievement was the use of solution deposition planarization (SDP) to gain CC yield contributing to an important cost reduction. Ink Jet Deposition (IJP) was used to scale-up the SDP production process for this novel ABAD architecture. Concerning RABiT substrates, an important achievement has been the demonstration of the suitability of using Ni 9%atW as a non-magnetic substrate with a high crystalline texture. In both cases adapted robust CSD buffer layers were developed.
Novel eco-friendly (low F) YBCO precursors for low cost CCs based on CSD have been validated to go to a scale-up stage for pristine and nanostructured CCs. A significant achievement has been to demonstrate that inks with a reduction of F content up to 80 % can be used with IJP with a final thickness of 1.2 µm achieved with single deposition and 1.6 µm with double deposition. These compositions have been successfully used in the reel-to-reel IJP route to CCs based on ABAD and RABiT substrates (up to 300 m in length). In the case of ABAD substrates and PLD YBCO deposition CCs in excess of 600 m have been demonstrated with high performance. Quality control tools such as in-situ optical measurements and ex-situ Hall mapping have been implemented to enhance yield and throughput.
Within the objective of creating nanocomposite CCs, the consortium has been very successful creating new approaches based on CSD and PLD. After the use of complex solutions a novel CSD approach was developed based on solution prepared well dispersed preformed nanoparticles with controlled sizes. Once stabilized as colloidal alcoholic inks they can be used for CSD YBCO growth. Suitable compositions (ZrO2, HfO2, BaZrO3, BaHfO3) were found leading to high performance nanocomposite CCs with enhanced control of performance and manufacturing. Highly epitaxial CSD nanocomposite REBCO (RE=Y, Gd) films were grown from complex or colloidal solutions. The main objective of controlling the final size of nanoparticles and defects associated to them (intergrowths, clustered vacancies) to enhance the vortex pinning force has been achieved. The novel colloidal solutions can now be used in the continuous CC reel-to-reel manufacturing process using IJP.
Very significant progress was also made in the development of self-assembled YBCO nanocomposite CCs by PLD based on BaHfO3 (BHO) and Ba2YNb0.5Ta0.5O6 (BYNTO) nanorods and associated defects. Several combinations of double perovskites with Y2O3 and the laser repetition rate were used to tune the pinning landscape at low and high temperatures on single crystalline substrates. The knowledge generated was transferred to metallic substrates and excellent performances demonstrated, particularly, worldwide record values on Ic were achieved at ultra-high magnetic fields and low temperatures on ABAD CCs (Bruker). The whole research activities on the properties of nanostructured CCs was baked with extensive use of advanced superconducting and Scanning Transmission Electron Microscopy investigations which were essential tools to guide in the overall development of high performance nanostructured CCs.
Finally, the project has developed a new type of round wire (CORT, Conductor-in-Round-Tube) based on RABiT or ISD CC tapes helically wound on a 1 mm thick Cu tube with a total diameter of 5 mm. A manufacturing process was defined and it was shown that these wires could lead to breakthroughs in CC applications in various areas of electric power engineering.
Project Results:
1. CHEMICAL SYNTHESIS APPROACH TO STABLE SOLUTIONS OF NANOPARTICLES IN ALCOHOLIC MEDIA
One of the outstanding objectives of EUROTAPES was to create a completely new chemical route to superconducting nanocomposite films based on the use of preformed oxide nanoparticles and colloidal solutions of them with the YBCO metalorganic precursors. This objective required the development of novel methods of oxide nanoparticle preparation with specific oxide compositions being compatible with the YBCO growth. These nanoparticles should fulfill strict requirements in terms of size, they should be highly dispersed and they should be stable in alcoholic media, i.e. the solvents being used in the YBCO solutions. The partners involved in these tasks were UAB, UGENT, ICMAB and TUC.
The colloidal solutions were prepared with high reproducibility using thermal, solvothermal or microwave heating of metallic salts which produced nanocrystals with sizes in the range of 4-10 nm and they had in many cases well developed crystal facets and they remained well dispersed in alcohols. Many different compositions were analyzed and its compatibility with the YBCO growth conditions determined. Several compositions belonging to three different oxide families were prepared: 1/ spinel MFe2O4 (M=Mn, Co) ferrites; 2/ fluorite phases MO2 (M=Ce, Zr, Hf); 3/ perovskite phases BaMO3 (M=Zr, Hf, Ti).
There were two main concerns concerning the behavior of these nanoparticles. One was its stability when a colloidal solution using Y, Ba and Cu metalorganics salts as precursors was prepared; another one was its chemical stability versus the YBCO structure when the film was growing to achieve an epitaxial film. A good stability (several months) of colloidal solutions with high concentration (up to 50 mol %) was achieved in highly ionic TFA and low-F YBCO precursors in all cases. Steric (using Triethylenglycol, nonanoic and decanoic acid ligands) and charge stabilization approaches were followed. All these stable colloidal solutions were used to grow highly epitaxial YBCO nanocomposites.
The second concern of chemical reactivity of the nanoparticles had a strong influence on the desired characteristics and compositions of the selected nanoparticles. Even if a considerable progress was made in improving the chemical compatibility of spinel phases with YBCO (particularly with CoFe2O4), this composition was finally discarded because a certain amount of metal substitution occurred into the YBCO structure reducing the superconducting transition temperature Tc. The fluorite phases were found to be reactive as well, leading to a final formation of perovskite phases BaMO3 (M=Zr, Hf, Ce) but this reaction preserved the superconducting properties of YBCO (Tc was not reduced) because the used metals (Zr, Hf, Ce) do not substitute the Cu positions in the crystalline lattice. A considerable effort was made to control the size, concentration and dispersion of these nanoparticles to analyze the influence of these parameters on the final micro and nanostructure of the YBCO nanocomposites. The main conclusion is that due to the chemical reactivity of the initial fluorite MO2 nanoparticles with the BaF2 formed after the initial decomposition of the Fluorinated precursors there exists always some nanoparticle coarsening and so the final size of the nanoparticles inserted in the YBCO matrix was always larger than the initial ones, i.e. it became cumbersome to keep a full control of the final size of the BaMO3 (M= Zr, Hf, Ce) nanoparticles.
To achieve further control of the final nanoparticles size within the YBCO nanocomposite it was decided to investigate the routes to prepare preformed BaMO3 (M=Zr, Hf, Ti) nanoparticles which we should expect to be non-reactive with the YBCO precursors and, very likely, an additional control of the nanoparticle size, shape, concentration and dispersion should be achieved. The synthesis of the perovskite nanoparticles was made through solvothermal reactions of the corresponding metal hydroxide and alkoxide in a glycol solvent. By selecting the capping ligand it became possible to achieve cube-like nanoparticles with homogeneous dimensions varied in a controlled way within the range of 4-10 nm. The influence of synthesis and washing conditions on the final nanoparticles size, stability and dispersion degree were carefully analyzed when they were exchanged into the YBCO alcoholic solutions. The success of obtaining such perovskite nanoparticles in alcoholic media is a real breakthrough which should have a strong influence on the final competitiveness of the solution colloidal approach to prepare superconducting nanocomposite coated conductors. We have already demonstrated that epitaxial YBCO-BaMO3 (M= Zr, Hf) nanocomposite films have very appealing superconducting performances and also that the process has a strong attractiveness concerning its scalability because the nanoparticle coarsening is very limited. This feature is very important when large film thickness needs to be prepared and so longer thermal annealing times are required.
In conclusion, the success in preparing oxide nanoparticles through solution approaches which can be used in colloidal solutions of YBCO films has been demonstrated for the first time and the attractiveness of this novel methodological approach to prepare complex nanocomposite thin films has been demonstrated. The novel methodology goes well beyond the interest in the area of superconducting materials and it can be certainly extended to many additional functional materials where enhanced performances or multifunctional behavior would become possible.
2. NEW ROUTES TO ADVANCED CSD NANOSTRUCTURED THIN FILMS AND COATED CONDUCTORS
The development of advanced approaches to chemical solution deposition (CSD) of nanostructured YBCO thin films and coated conductors was a highlight of the EUROTAPES project. The main goals were, first of all, to switch from a full use of fluorinated metal-organic precursors of Y, Ba and Cu to new eco-friendly inks with a reduced content of Fluorine. These inks should then be adapted for the use in Ink Jet Printers (IJP) and also to become colloidal solutions incorporating the preformed oxide nanoparticles which should lead to superconducting nanocomposite films and coated conductors. ICMAB and KIT were the main partners involved in this task.
A certain variety of low fluorine (up to 80 % of F reduction) precursors were successfully prepared and its suitability investigated. All the prepared solutions were composed of the same precursor salts (Yttrium trifluoroacetates, Ba and Cu acetates) which were dissolved in mixtures of an alcohol (methanol or butanol) and propionic acid or just propionic acid. Some of them were useful for optimizing the thick film growth process (up to 1.2 µm) using multideposition. Other solutions were optimized to maximize single deposition using IJP (up to 1.1 µm) which could lead to films of 1.6 µm using double deposition. In all cases optimizing the pyrolysis process was an important issue to achieve high reproducibility, a high degree of film homogeneity and a smooth surface. Complementary studies of thermal decomposition and In-situ optical and thermomechanical analysis were extremely useful to achieve wide understanding of the complex film evolution during pyrolysis. All these processes were successfully extended to the case of colloidal solutions using preformed nanoparticles.
Once the process to prepare homogeneous REBCO (RE= Y, Gd) precursor films was completed a wide effort was made to define the optimal conditions to grow epitaxial films with large total critical currents Ic, i.e. with large film thicknesses and high critical current density Jc. Two main difficulties were identified: one is that the degree of supersaturation (and therefore the nucleation and growth rates) in the REBCO growth process changes with film thickness (gas – solid reaction depending on the H2O and HF partial pressures at the growth interface). The second difficulty arises from the fact that it may appear some interfacial reactivity with the CeO2 cap layer mostly used as cap layer in coated conductors. In that case a degraded epitaxy would appear with the corresponding decrease of Jc.
Several strategies were followed to achieve some control of the supersaturation conditions, based on modified parameters (mainly temperature, heating ramp, H2O partial pressure and Ag additives). The largest performances achieved in the CSD route were for a 1.2 µm YBCO film grown on LaAlO3 substrates with Jc(77K)(sf) of 2 MA/cm2 (Ic(77K) = 240 A/cm-width). Values close to those were also achieved in YBCO + BaZrO3 nanocomposites using single IJP deposition: Jc(77K)(sf) = 2.7 MA/cm2 (Ic(77K) = 229.5 A/cm-width). It was also shown that very promising performances can be achieved in (Y,Gd)BCO + BaHfO3 nanocomposite thin films, even if in this case no special efforts were made to enhance the film thickness beyond ~300 nm.
The low F solutions were also widely used to grow YBCO nanocomposites using the preformed nanoparticles approach. Once the MO2 (Zr, Hf) and BaMO3 (M=Zr, Hf) nanoparticles were stabilized with the corresponding inks to form colloidal solutions, it was demonstrated that, essentially, similar growth conditions could be used in the nanocomposite films as compared to the pristine ones, although some fine tuning was always necessary. A particular difficulty to be faced was that the nanoparticles display some tendency to be accumulated at the substrate interface, thus degrading the epitaxial quality. This problem could be solved by using YBCO seed layers which then promote homoepitaxial growth. Typically, YBCO nanocomposite thin films display very high performances at low film thickness (~300 nm): Jc(77K)(sf) = 4-5 MA/cm2 and a smoothed magnetic field dependence as compared to pristine films. Very remarkably, a load record of 20 % M could be achieved with non-reactive BaMO3 (M=Zr, Hf) nanoparticles which then maximize the vortex pinning properties.
Finally, optimizing the growth of REBCO layers on metallic substrates with CeO2 or Ce(1-x)ZrxO2 (CZO) cap layers required dealing with the reactivity issue (BaCeO3 formation through reaction of the cap layer with the BaF2 existing in the film precursor). It was demonstrated that to achieve high quality epitaxy the supersaturation conditions needed to be reexamined in order to maximize the REBCO nucleation rate which competes with the BaCeO3 formation. Here again the nucleation rate depends on the RE ion (Y or Gd) and film thickness and so the processing conditions (Temperature, H2O partial pressure, Ag content) needed to be tuned. Coated conductors on CSDCeO2/ABADYSZ/SS substrates achieved a high performance with a single 700 nm IJP deposition: Jc(77K)(sf) = 1.4 MA/cm2, (Ic(77K) = 98 A/cm-width). In the case of RABiT substrates high quality nanocomposite thin films were also demonstrated using a composition Y0.33Gd0.66Ba2Cu3O7 + 12% M BHO (Jc= 1.9 MA/cm2). The foreground knowledge associated to these promising performances was transferred to the industrial partners who are now in conditions to integrate the novel CSD processes in their corresponding manufacturing units.
In conclusion, the CSD approach to nanostructured superconducting thin films and coated conductor made worldwide pioneering advances strongly promoted by the multidisciplinary collaborations established within the scope of the EUROTAPES project.
3. MANUFACTURING AT THE INDUSTRIAL SCALE OF "ALL CHEMICAL" COATED CONDUCTORS WITH HIGH PERFORMANCE
Establishing good practices for industrial plants design and construction for coated conductor production based on an “all chemical” manufacturing approach has been a breakthrough of the EUROTAPES project. Two different companies have reached novel pilot lines for Chemical Solution Deposition (CSD) of buffer layers and HTS layers: Deutsche Nanoschicht GmbH (DNANO) and Oxolutia (OXO). DNANO has adopted a CC architecture based on RABiT substrates (CeO2/La2Zr2O7/NiW) while OXO uses the ABAD substrate produced by Bruker (Ce(1-x)ZrxO2/YSZ/SS). Both reel-to-reel (R2R) pilot lines have in common the use of the low Fluorine metalorganic precursors for YBCO films, however, the exact composition of the inks is different owing to the fact that the deposition system differs in both cases, as it’s described below.
OXO has designed and built two different pilot plants for R2R inkjet printing (IJP) deposition of thin films and put them in operation. The deposition system can feature at maximum speeds of 100 m/h, with tape widths of 30 mm using 512-nozzle piezoelectric printheads. The modular nature of the pilot plant allows for versatile, fast changes in inkjet conditions and drying or low temperature thermal treatments for the pyrolysis process. In 2017, an improved second pilot plant will be operative with more precise control of tape movement, enhanced resolution in droplet visualization and light-irradiation treatments A total number of 6 unit operations were included in the pilot line.
The pilot line was successfully used for inkjet printing the 20-nm thick ceria cap layer from special inks on ABAD-YSZ substrates from BRUKER. A high speed of 30 m/h makes the process competitive, taking also into account that it is made at atmospheric pressure, no vacuum is required. See figure 1.
Concerning the YBCO layer, inkjet printing was shown to be useful for obtaining superconductor films as thick as 1 micron by successive inkjet multideposition. For that goal, special inks were developed, which allows compatibility with industrial piezoelectric printheads and steady droplet injection. The deposition system being used can be still adapted to the new inks developed by ICMAB for IJP allowing to minimize the number of layer deposition and to prepare nanocomposite films. The deposited layers can be decomposed in the same R2R line. This pilot plant R2R system has also been used for deposition of CSD planarization layers in ABAD substrates, as described in Highlight No. 6, where lengths up to 10 m were produced. The ejection and size of the droplets can be monitored via a special docking position of the printhead assembly. See figure 2.
In another separate pilot plant, R2R growth of the YBCO pyrolyzed layers coming from the inkjet printing pilot line is carried out. Such plant is composed of air-tight feed and take-up chambers, a 3-meter long furnace and gas circuits. Special inserts allow for the correct conversion of 10-meters long YBCO superconducting tapes. A special design will soon allow for extending the growth to the 100 meters range. Apart from that, low pressure can be implemented up to 50 mbar. The whole system is controlled automatically through a Labview-interfaced SCADA system.
Moreover, quality control by optical microscopy and optical reflectometry with a 3 mm2 spot size and acquisition time of seconds, was shown to cope with industrial production of the chemical layers, except that of grown YBCO layer. See figure 3.
On 2016 the expanded pilot line of DNANO was inaugurated. It has started to manufacture all chemical solution coated (CSD) conductors on RABiT metallic substrates on regular basis in around 20 different devices for the several production steps all running in reel-to-reel processes. This includes all the steps of assembling the technical wire like substrate pretreatments, buffer film production, HTS layers as well as CSD silver contact layers, slitting to customized widths, and electrical and mechanical protection layers manufacturing which can be selected from electroplating with copper and lamination with metal foils depending on the target application. This new production line production enables DNANO to provide superconducting tapes in reliable high quality.
The plant increased the production capacity within DNANO by a factor of 50, but it is not running yet on 24/7 basis as an exclusive production facility as further technical adjustments to different applications as well as optimization in cost effective production methods is still ongoing in parallel to prototype production. Technical coated conductors in widths of 4-10 mm with customized shunts can be produced in typical length up to 100 m. Exceptional tape lengths up to 400 m can be produced. Wider tapes will be available in the future. Full inductive measurements of the whole length for 10 mm wide tapes as well as complete resistive measurements in 1.5 m steps can be provided.
Besides the offline control by X-ray diffraction (XRD) of the film texture by electron backscatter diffraction (EBSD) as well as precise control of physical and chemical properties of the precursor ink (like metal ion concentrations, rheology, and refraction index), the online drop watch-system can be a powerful tool to detect ink jet printing related variations of the film quality and homogeneity. Drop watch systems to control the constant ink release onto the tapes were considered to be important when the project plan was compiled. Experiments with drop watch systems from UCAM at DNANO showed that this successfully detects deviations from desired ink release, e.g. deviations in release direction at partially blocked nozzles as well as the total failure in case of completely blocked nozzles. But even when errors are detected in a very early state, this provides no appropriate solution to reset the printer by unblocking the nozzles without interrupting the printing process. However, any unblocking of the nozzles requires an interruption of the printing process for disassembling or at least cleaning and rinsing of the printhead. A more stable or self-resetting printing process was preferred. The slot-die process is much less susceptible to errors in printing related film homogeneity and it was used all during the last 3 years in D-NANO.
The permanent control of the oxygen partial pressure in the furnace exhaust gas during the crystallization annealing turned out more effective, because a (still manual triggered) feedback control loop on this parameter can be operated without stopping the running process and the relevant times for changes in the inlet gas composition or amount are in the range of several 10 minutes.
During the tape assembling process, starting from the first oxygen annealing after the YBCO crystallization, the critical current is detected via the so called Tapestar device from THEVA in a R2R process. However, the most significant quality control tool is the final R2R transport critical current measurements when a technical tape is finally fully assembled.
4. DECIPHERING THE NANOSTRUCTURAL FEATURES RESPONSIBLE OF THE ENHANCED PERFORMANCE OF NANOCOMPOSITE FILMS PREPARED BY CHEMICAL AND PHYSICAL DEPOSITION METHODOLOGIES AT DIFFERENT MAGNETIC FIELDS AND TEMPERATURES
Creating nanocomposite superconducting films and coated conductors with high performance was a key objective of the EUROTAPES project. To achieve this goal requires a full understanding of the mechanisms underlying defect creation in these films and how we can control the complex nanostructure of the REBCO films derived from the two different processing methodologies used in the project: Chemical Solution Deposition (CSD) and a Physical deposition methodology (Pulsed Laser Deposition, PLD).
An extensive use of advanced nanostructural characterization techniques was an essential requirement for the success of the project. Scanning Transmission Electron Microscopy (STEM) combined with Energy Dispersive X-ray (EDX) and Electron Energy Loss Spectroscopy (EELS) chemical analyses, as well as 3D electron tomography, were tools which provided many details of the defect structure, from the micrometric to the atomic scales. The partners with strong involvement on these tasks were UA, ICMAB and IFW. Covering these different length scales is a very important issue to be able to correlate the structural features with the superconducting performances. Actually, the project focused its interest onto three different regions of the magnetic phase diagram (low, medium and high temperatures) where it’s expected that the dimensions of the defects controlling vortex pinning and percolating critical currents through a low angle grain boundary network are modified, owing to the temperature dependence of the superconducting characteristic lengths (coherence and penetration lengths). Therefore, deciphering the nanostructure features responsible of enhancing the superconducting properties is a complex objective requiring a systematic correlation of STEM and physical properties measurements onto the same samples. Advanced measurements of physical properties were investigated by TUW, ICMAB, IFW, ENEA, UCAM and KIT.
There exist an essential difference in the growth mechanism of REBCO nanocomposites of CSD and PLD causing a completely different final nanostructure. CSD is an ex-situ growth technique where the epitaxial YBCO film grows after the secondary phase nanoparticles have been formed, both in the case of complex solutions where the nanoparticles are spontaneously segregated and in the case of preformed nanoparticles. In the case of PLD nanocomposites growth of YBCO and secondary phases occur simultaneously through evaporation of all the atomic species and this is an essential ingredient to achieve self-assembly of nanoobjects (nanorods for instance). This essential difference among both approaches lead to a separate analysis of the corresponding nanostructures.
In the case of CSD nanocomposite films the most relevant feature is the analysis of the crystal structure, size, shape, distribution, crystalline orientation and interfacial quality of the secondary phase nanoparticles. A systematic analysis of these features in spontaneously segregated nanoparticles (BaZrO3, BaYTa2O6) and preformed nanoparticles (BaMO3, M=Zr, Hf) was carried out. For instance, STEM analyses of nanocomposites based on preformed spinel nanoparticles immediately revealed that novel double perovskites, such as YBaFe(2-x)CoxO5 or YBaCuFeO5, were formed thus indicating a strong reactivity with the YBCO precursors. In the cases of fluorite and perovskite preformed nanoparticles the final nanophases (BaMO3, M=Zr, Hf) had sizes in the 10-30 nm range and it became very useful to ascertain how they were distributed within the film to ascertain its growth mechanism. It was clear, for instance, that an excessive concentration of nanoparticles at the interface lead to a degraded epitaxy of the YBCO films. Observing sharp interfaces among a seed YBCO layer and YBCO+BZO films helped to understand the positive role of homoepitaxy at high nanoparticle concentration. From the observation of the final size and distribution it was concluded that non-reactive particles display little coarsening and they can avoid agglomeration at least up to 20 % M. Another very important feature, fully analyzed by STEM, was the influence of nanoparticle features and processing steps on the induced defects within the YBCO matrix, particularly the YBa2Cu4O8 (Y248) intergrowths. These intergrowths are responsible of the increased nanostrain determined by X-ray diffraction, mainly due to the partial dislocations surrounding them, and so their final length was found to correlate with high temperature vortex pinning efficiency (strong and isotropic pinning) in the nanocomposite films. Several important parameters were found to correlate with the intergrowth density and length: orientation randomness of the nanoparticles, size and density of the nanoparticles and also kinetic features of the YBCO growth process (heating rate for instance). The observed features and the derived conclusions were essentially valid for both preformed and spontaneously derived nanoparticles, even if in the first case a smaller size and a higher concentration can be achieved.
An additional feature discovered in the scope of the EUROTAPES project was the atomic scale structure of what it was believed to be Y248 intergrowths. These defects were early detected in YBCO films and they were associated to a novel interlayer structure of the high temperature superconductors. In the YBCO nanocomposite films a very density of such intergrowths was very often observed which lead to what it was conceived as a “stoichiometry catastrophe”, i.e. the local structure was extremely different of the expected Y123 structure. The reality is that STEM combined with DFT calculations and XMCD synchrotron analyses showed that there exists a high concentration of Cu-O clustered vacancies in the double chain of the expected Y248 structure which then recovers the initial Y123 stoichiometry. These defects were shown to have ferromagnetic order and considering that their dimension is below aprox.1 nm, they are expected to influence the low temperature (T< 20 K) vortex pinning efficiency (weak and isotropic pinning). The relevance of intergrowths in the twin boundary structure of nanocomposite films was also determined and correlated with the strong anisotropic vortex pinning contribution close to the Irreversibility Line in these films. In conclusion, CSD nanocomposite films display a very complex nanostructure and EUROTAPES deeply contributed to advance in our understanding of its correlation with processing features and physical properties.
In the case of PLD films mainly BaHfO3 (BHO) and Ba2YNb0.5Ta0.5O6 (BYNTO) inclusions inside the YBCO matrix were studied. A high density of c-axis oriented BYNTO columns with a mean diameter of about 10 nm evenly distributed in the YBCO matrix was grown on single-crystal substrates at low growth rates. These structures lead to extremely high pinning forces and distinct features in critical current anisotropy Jc(Ɵ). Furthermore, we were able to adjust the orientation and distribution of BHO or BYNTO nanoparticles in thick YBCO films grown on technical templates. BHO grows typically in fan-shaped manner, increasing the pinning in broad range around H||c and flattening the Jc-anisotropy. Increased growth rates and substrate temperature lead to straighter alignment of segmented columns and the formation of ab-parallel BHO/Y2O3 platelets and Y248 intergrowths. BYNTO doped films show a mixed-type structure of shorter BYNTO columns parallel c and BYNTO/Y2O3 platelets in ab-direction having a higher thickness with increasing substrate temperature. Both kinds of platelets enhance pinning for H||ab. Finally, BHO doped YBCO films were grown on miscut single-crystalline substrates with vicinal angles Ɵ up to 40°. It was found that the growth mode switches from c-axis-oriented BHO nanocolumns (Ɵ = 0°) via a mixed distribution of c- and ab-aligned features (Ɵ = 2-10°) to purely ab-parallel BHO/Y2O3 platelets. These platelets adopt the vicinal angle of the substrate and act current blocking, increasing the anisotropy of the critical current in longitudinal and perpendicular direction.
Finally, we should also mention that STEM analysis (together with FIB sample preparation tools) of many coated conductors (ABAD and RABiT substrates) processed by CSD or PLD under different conditions at the industrial scale were very useful to ascertain the influence of specific manufacturing parameters on the micro and macroscopic defect structure development which may degrade the percolating critical currents. This includes grain boundaries, large precipitates, voids, misoriented grains, etc. and the local structure analysis could be very efficiently correlated with macroscopic physical properties characterization (transport and inductive measurements, Hall effect imaging). In conclusion, the extensive effort made in EUROTAPES in correlating local structure to physical properties and processing was a critical issue to the success of the project in developing high performance materials.
5. HIGH GROWTH RATE APPROACHES TO TUNED SELF-ASSEMBLED NANOCOMPOSITE STRUCTURES IN THICK FILMS BY PULSED LASED DEPOSITION
The analysis of the mechanisms to generate nanostructured CCs to enhance vortex pinning in PLD-grown YBCO thin film was widely investigated by several partners (IFW, ENEA, UCAM) within the EUROTAPES consortium, by combining different processing conditions, metallic substrates and compositions. The main issue in PLD grown nanocomposites is to define the composition of the secondary phase to be used (usually non-superconducting perovskites or double perovskites) and how these secondary phases self-assemble within the YBCO matrix. The main nanostructures usually observed are columnar nanorods (diameters in the range of ~5 nm) which may display a certain degree of splay, nanoplates and induced planar defects (Y248 stacking faults). After an initial screening of the most promising secondary phases, the consortium decided to center its effort in understanding the mechanisms to form nanorods based on BaHfO3 (BHO) and Ba2YNb0.5Ta0.5O6 (BYNTO). The YBCO nanocomposites based on these phases were grown first on single crystals and later on ABAD-YSZ and RABiT Ni-W substrates. The influence of films thickness and growth rates on the nanostructure was determined in conventional PLD growth. Also, novel processing approaches based on the formation of intermediate liquids during growth were investigated to further enhance the YBCO film growth rate.
IFW particularly studied the growth of undoped, BHO doped and BYNTO doped YBCO films with a thickness of up to 8 µm on industrially prepared metallic templates, such as buffered RABiT Ni-W substrates (from DNANO) or ABAD-YSZ based substrates (from BRUKER) using PLD with growth rates of up to 4 nm/s. In general, BHO/BYNTO additions to the YBCO matrix result in an elongated c-axis length and a densified YBCO microstructure by refining Y2O3 inclusions. Whereas a decrease of Jc is observed in undoped films with thicknesses above 2 µm due to misoriented YBCO grains originating from defects, as for example large Y2O3 particles. Such misoriented regions are found mainly in films with thicknesses higher than 5 µm in doped films. Both dopants act as strong artificial pinning centers and increase the pinning force density FP and irreversibility field Hirr. It was found that a higher growth rate leads to a transition in the microstructure of BHO-doped YBCO films, switching from long c-axis oriented nanorods to a more complex structure with short nanorods and ab-oriented platelets. This results in a change of the Jc anisotropy, from a large c-axis aligned pinning contribution to a more isotropic Jc(B,Θ) dependence.
ENEA focused on the PLD deposition of YBCO with BYNTO as c-axis oriented nanocolumnar inclusions on CeO2/YSZ/SS ABAD metallic templates from Bruker. The proper BYNTO columnar growth was achieved through a multilayer approach, using a seed layer of pure YBCO at the interface between YBCO-BYNTO and the ABAD substrate. The YBCO seed layer was introduced for the passivation of the CeO2 layer, having a high surface roughness (~5 nm – AFM analysis), and for roughness mitigation. TEM investigations carried out by UA clearly indicate the development of columnar BYNTO system embedded into the YBCO matrix. Thin YBCO-BYNTO nanocomposite films were deposited on YBCO seed layers with small thicknesses (~7 - 60 nm). In particular, YBCO-BYNTO films grown over YBCO seed layers showed an evident correlated contribution in the angular behaviour of the critical current density. This contribution due to the columnar growth of BYNTO in the YBCO matrix is active in the low-to-mid magnetic field range (0.5 – 3) T and evident in the temperature range (50 – 77) K. At the same time, the in-field study of transport properties in the configuration with the magnetic field applied parallel to the YBCO c-axis revealed very good low temperature behaviour with pinning force densities close to 500 GN/m3 at 12 T and 10 K.
BRUKER focused on the optimization of obtaining YSZ-ABAD CCs with the highest pinning force at low temperatures (4.2 K) and ultrahigh magnetic fields (> 18 T). They were able to generate a novel nanostructure combining BZO nanorods with a fan-shaped distribution and pressure triggered stoichiometric variations. Strain maps obtained through STEM investigations by UA showed that the nanorods generate a dense nanostrain within the YBCO matrix. This advanced nanostructure demonstrated to lead to the highest critical currents achieved so far under these conditions (Ic(4.2K,18T)= 1250 A/cm-w for 22 m), even in long length conductors (Ic(4.2K,18T)= 1000 A/cm-w or Ic(4.2K,5T)>2500 A/cm-w for 600 m).
Finally, UCAM focused on controlling the growth of the YBCO matrix with 5 mol% BYNO nano-inclusions at very high growth rates with the goal of having high in-field critical current Jc(B,Θ) at low cost. At low YBCO PLD growth rate (~1 nm/s), an immiscible secondary phase (BYNO) tends to be well self-assembled into (vertical) nanorods, (horizontal) nanoplates and/or nanoparticles coherent with the matrix, contributing accordingly to an increased Jc(B,Θ) through the flux pinning effect in the relevant directions. At higher growth rates, surface diffusion, of the ablated and deposited PLD material, becomes the limiting factor for the good YBCO epitaxy and BYNO self-assembly. Building-up on earlier knowledge of liquid assisted growth, UCAM developed an in-situ process of Liquid-in epitaxial (LiE) growth. In this case the growing YBCO with BYNO has small amount liquid phase component (Y-BaO-CuO) added during the deposition and "consumed" during the growth. As a result, on (100) SrTiO3 substrates, at very growth rates (>15 nm/s, i.e. ~1 µm/minute), an extraordinary increase in Jc(B,Θ) has been obtained, compared to standard PLD growth. Invoking different growth modes of the self-assembled BYNO, tuning of the Jc(B,Θ) has been achieved by modifying growth temperature, hence having Jc anisotropy from c-axis aligned pinning contribution to more isotropic Jc(B,Θ). Similarly, on YSZ-ABAD metallic substrates (from Bruker), Jc(B,Θ) in LiE films were comparable to the results for usual PLD films grown at 10 times slower rate. Jc(B,Θ) was not thickness dependent for films as thick as 2 μm, indicating there is no thickness limit to be expected.
In conclusion, PLD growth of YBCO nanocomposites was very widely investigated within the EUROTAPES project using the metallic substrates generated by the industrial partners and a large body of knowledge was generated allowing to optimize the superconducting properties at different temperatures and magnetic fields.
6. MANUFACTURING AT THE INDUSTRIAL SCALE OF HIGH PERFORMANCE COATED CONDUCTORS BASED ON ABAD SUBSTRATES IN THE ISD APPROACH
Full manufacturing plant was established to enable an industrial scale manufacturing of >600m long HTS coated conductor by BRUKER based on YSZ-ABAD substrates. The main innovative idea for the HTS film deposition is based on a double disordering (DD) mechanism of YBCO nano-structure where (i) an intrinsic disorder is caused by periodic modulation of oxygen pressure during high-rate pulsed laser deposition (HR-PLD), and (ii) an extrinsic disorder is activated via injection of nanoparticles of a foreign material added to the composition of the ablated target.
Double-disordered YBCO layer has been shown to display the highest critical currents in magnetic field (Ic>2500 A cm w at 5 T, perpendicular field at 4.2K).
An up-scaled (>600m length) HR-PLD machine was developed and employed for tape manufacturing of CCs with nanostructured HTS layers. See figure 4: PLD up-scaling: PLD 600. See figure 5: View of drum with helical winding: 610 m long tape after deposition of HTS layer.
Corresponding processing stations of the plant at BRU included tape polishing, planarization (OXO), ABAD buffering, HR-PLD for DD-YBCO processing, as well as metallization of the tape via deposition of silver protection layer and further galvanic plating with copper.
The main manufacturing steps were adjusted to the throughput of 40 m/h and a continuous production cycle of >48 hours.
Very important initial steps of tape processing are long tape polishing and quality control via automatic imaging of tape surface. Surface quality determines homogeneity of critical current within the long length tapes. Sufficient surface quality can be provided by planarization of the substrate via an additional oxide amorphous layer achieved by solution deposition planarization (SDP).
The idea of planarization layers on metallic rough substrates produced by reel-to-reel inkjet printing was successfully demonstrated up to a length of 100 meters and speeds close to 40 m/h by OXO. In short samples, inkjet-planarized rough unpolished stainless steel substrates rendered an Ic of 50% that of fully polished stainless steel. This indicates the huge potential for cost reduction in coated conductors with ABAD-architectures since the time-consuming and costly polishing step is avoided by the deposited layer from inks at high speeds.
Planarization oxide layers between the metallic substrate and ABAD-textured YSZ layer were manufactured in industrially-meaningful lengths (100 meters). OXO and ICMAB closely collaborated with BRUKER towards the definition and realization of high-performing cost-effective coated conductors in long lengths.
In addition, epitaxial flat ceria buffer layers were also deposited on ABAD-textured YSZ in the reel-to-reel inkjet printing pilot line at OXO at speeds as high as 30 m/h and maximum lengths of 10 meters. This approach might also be an industrial possibility to integrate in the manufacture of coated conductors in terms of better control of the morphology of the buffer layer. ICMAB had also an important involvement in the task.
For >600m tape lengths, as a temporary technical solution, a physical vapor deposition of alumina-YSZ combined layers was used by BRU before the SDP technology of planarization is up-scaled to the 600m lengths.
An upscaling of technological equipment at Bruker was performed together with the implementation of Quality control tools and finally Quality Control System and other “tools” developed within the EUROTAPEs project. One of the outstanding features here is implementation of an Ultra-High-Speed PLD that leads to a substantial benefit in feasibility of tape production.
As a result, 609 m long tapes manufactured via proof-on technology for ABAD based architecture meet the main project requirements. These are the longest CCs in Europe fabricated so far; the critical currents in high field are at the champion level worldwide (data of FHMFL, Tallahassee). See figure 6: Process up-scaling (architecture 1, end pieces of 602-609 m long tapes). Recent measurements at Tallahassee, Jan 24, 2017, D. Abraimov, D. Larbalestier width of the tape corresponds to 4 mm.
Cost assessments performed also for different tape applications result in rather optimistic numbers, well acceptable for various technical fields.
At the beginning of the Eurotapes project THEVA finished assembling its fully automated pilot line based on the Inclined Substrate Deposition (ISD) approach and started the regular production of CCs. The tape length was 60 m. After stabilizing a good production yield for a sufficiently high performance class (Ic~300 A/cm-width), THEVA started a development program to increase the tape length to 600 m. The goal was to:
• increase process speed,
• improve material efficiency,
• improve reliability of the machine components and reduce demand for maintenance,
• improve film quality by optimizing deposition parameters.
THEVA uses an all electron beam evaporation approach, meaning that all individual layers of the coated conductor are deposited by electron beam evaporation. This allows focusing the development on only a few major components. The results can then be applied to all processes and production machines. To ensure high yield and constantly good quality over the whole tape length of 600 m, all components must not fail over a process time of at least 20 h. Also, all process parameters need to be constant over the same time.
In 2016, THEVA introduced three-shift operation to its production to cover the long deposition times and additional maintenance work. With the first improvements in place the tape length to be processed was increased to 350 m. Tape performance and yield was maintained at the same level as with 60 m process lengths. In the first quarter of 2017, the tape length was increased to 600 m in the superconductor process and to 1200 m in the buffer layer processes. For this the tape speed in most fabrication processes was enhanced by at least 50%. This major step required significant changes especially to the evaporation system. E.g. the e-gun emitter design was improved to reduce wear and ensure long operation times. Also, the evaporation system was altered to increase material efficiency by 60%. The design of almost all vacuum components was revised to eliminate time-consuming maintenance.
To stabilize process parameters, the level of automation of the pilot line was enhanced. Deposition rate is now controlled automatically to keep a constant film thickness. Additionally, new sensors to measure tape temperature and thickness of metal layers were developed to have better control over these quantities. Last but not least, THEVA was closely working together with its suppliers to improve the quality of the raw materials. This and further optimizations to all processes now make it possible to reach tape performances of 500 A at 77 K in self field in 12mm wide tapes with a production length of 600 m.
7. ROUND WIRE PRODUCTION METHODOLOGY BASED ON COATED CONDUCTORS (CONDUCTOR ON ROUND TUBE, CORT)
In the Coated Conductors (CCs) based on the high-temperature superconducting material REBCO a metallic substrate tape (stainless steel, Hastelloy, NiW alloy) is covered by a thin layer of REBCO and eventually it’s finally covered by protective metallic layers (silver, copper). Therefore the CCs tapes have a form that is rather different from the round or oval wires and cables made from normal metals or low-temperature superconductors. Production of round wires from CC tapes would be a break-through in the CC application in various areas of electric power engineering because the technology already developed for low-temperature superconductors could be used directly or after minor modifications.
Attempts to deposit a superconducting layer directly on a round substrate did not lead to conductors of sufficient transport capacity. Therefore in the EUROTAPES project we have developed the concept of round wires made of CC tapes helically wound with the lay angle Ɵ on a round core with diameter Df. See figure 7.
During the project execution the alternative of using a metallic tube as the central core emerged as the most promising because of several advantages. Copper tube of ~1 mm wall thickness is on one side tough enough to offer necessary mechanical support for the tapes but on the other hand it is flexible enough to allow winding of coils with the diameter as small as 100 mm. Moreover such arrangement for which we started to use the abbreviation CORT (Conductor-in-Round-Tube) provides the possibility to use the central tube as a channel for the flow of coolant that could be e.g. liquid nitrogen or gaseous helium. We have also verified that an insulation from polymeric foam could arrange for sufficient thermal insulation of a single wire used for current transport. In case of coil a collective covering of all the winding turns the coil would become lightweight and compact.
Application of CC tape for the production of CORT round wire requires to test first the tape properties in order to identify the critical parameters limiting the geometry of tape arrangement in the wire. In particular the deformation of tapes by wrapping around round core leads to certain reduction of critical current at too small diameters. At IEE the rig for in-situ testing of critical current degradation at tape wrapping has been developed and 4 mm wide tapes from two commercial manufacturers (Superpower, Sunam) as well as from two project partners (DNANO, THEVA) investigated in liquid nitrogen bath. Wire diameter of 5 mm can be achieved in this kind of wire architecture.
Important parameter in the wire manufacturing is the pulling force exerted on individual tapes. With this force the flat tape is deformed to follow the cylindrical surface that for the first layer is a smooth round core. However in the successive layers the tapes are forced to accommodate to the outer surface of previous layer of tapes that commonly contains gaps between tapes and also sharp tape edges. For each of the tapes used for CORT manufacturing first a short (0.5-1 m) model was prepared by hand, using the procedure that keeps constant the selected pulling force. Testing of such models in liquid nitrogen revealed that CC tapes of various architectures and prepared by different technological procedures require rather different pulling forces in order to achieve a regular lay-out of the wire without substantial degradation of its critical current.
CORT round wire with the length exceeding 100 meters can be manufactured using the machine that was developed during the project. Currently it contains two carousels, each accommodating 4 CC tapes on supply spools. Set of guiding wheels leads the tapes under desired angle and with the preset pulling force on the central core that is moving with the speed controlled by an independent drive. Each of the two carousels is rotating by the action of its own drive. The total of 3 drives is controlled by the software that secures perfect coordination of movements during all the steps of CORT winding. Photo of the machine follows: See figure 8.
This machine was utilized to produce several samples of CORT round wires from tapes delivered by the project partners. The picture showing the test in liquid nitrogen bath of the 3 meters long round wire made from 8 tapes is below: See figure 9.
The advance in mass production of 4 mm class tapes by European tape producers (THEVA and DNANO are our partners in this activity) is a pre-condition for further progress towards a complete wire with all the necessary accessories (envelope, terminations, sensors,...).
8. CONTINOUS EX-SITU QUALITY CONTROL SYSTEM BASED ON HALL EFFECT MAGNETOMETRY
The critical current is the final figure of merit of a coated conductor. It is hence mandatory to ensure a nominal value along its entire length as a final quality control. Although different applications are operating at different fields and temperatures and the critical current is important for them only under these conditions, the assessment of the critical current at liquid nitrogen temperature and low fields is often sufficient for quality control since deviations from the standard performance due to irregularities during production harm the critical currents at all fields and temperatures. There are two common methods for measurements of the critical current in long length conductors. Firstly, a direct injection of an increasing current on a short segment (typically one meter) of the tape until a voltage is detected. This method directly probes the critical current without any modelling. However, the application of the needed (large) currents is demanding and the spatial resolution is low, essentially given by the length of the tested segment, which cannot be made arbitrarily short because a tradeoff between measurement time and spatial resolution has to be made. For these disadvantages, a magnetic assessment of the critical current is made instead in most cases. THEVA is offering a commercial system for this purpose, called TapeStar, which is in use at nearly all commercial producers and many research institutions. The currents are not applied by an external source in this device, but induced by a local magnetic field. These currents in turn generate a magnetic field, which is recorded by a linear array of Hall probes. The obtained field profile is then compared with the ideal one to estimate the critical current. The method is well suited for the identification of defects along the length of the conductor, quantitative predictions of the local critical current on the other hand need a calibration with resistive measurements of a reference tape and fail if the field profile deviates strongly from the ideal one.
A new evaluation algorithm for measurements performed by THEVA’s TapeStar was developed by TUW with the aim of improving the quantitative prediction of the critical current and, even more important, get full benefit of the high spatial resolution of these measurements. The linear Hall array offers the possibility to assess variations of the critical current not only along the tape with a resolution in the millimeter range, but also the distribution of the current density across the width of the tape. This information is very valuable for the identification of problems during the tape production and for predicting the performance of the conductor after slicing to tapes of smaller width or filamentization. Although the measured data contain local information of the magnetic field the underlying current density is not unique, because of the non-locality of the problem. The field profile is recorded only along one line, but the currents flowing in the vicinity of this line are contributing to the field at the positions of the Hall probes as well; thus, in a first step, the geometry of the induced current loops had to be determined to separate the local information.
It turned out that the calculated local current depends significantly on the chosen mesh for the discretization of the current density within the tape. This made the solution unstable against variations of the tape position with respect to the Hall sensors as well as changes of the effective width of the superconducting layer, which is not necessarily the same as the geometric width of the tape and may even change along the tape. An adaptive local mesh was introduced to solve this issue and provides, as a side effect, an estimate of the error of the derived current density. One example of the derived critical current densities is shown in the figure.
See figure 10: Test measurement of a short piece of coated conductor. The absolute value of the critical current density is shown in the uppermost panel, its components parallel and perpendicular to the tape are displayed in the panels below. The bottom panel contains the error estimation.
Improvements of the Tapestar sensor system were developed in order to get a good quality of the measurement. For example, the distance between the sensors was minimized to improve the resolution and the horizontal position of the sensors was controlled with maximum accuracy.
The new evaluation algorithm together with the optimized sensor system can now be implemented in an improved version of the Tapestar System. This would then give unsurpassed data quality for R&D as well as routine quality inspection of HTS wires in a production plant.
9. NEW METALLIC SUBSTRATE COMPOSITIONS BASED ON NIW AND CU ALLOYS
The development of novel Cu substrates where the poor mechanical properties of RABiTTM Cu substrates are overcome as well as qualifying new highly textured, non-magnetic NiW substrates with a tungsten content around 9% are outstanding objectives of EUROTAPES.
For Substrates based on Cu-alloys solution hardening was the method of choice for the production of a more economic metallic substrate with reduced magnetism with respect to the currently available Ni-5at%W substrate. LFL and ENEA showed that the most promising candidate to be alloyed with copper with suitable cube texture was germanium, while nickel was improving mechanical properties. The composition achieved with excellent texture and slightly improved mechanical properties was CuNi10%Ge0,8%.
The binary alloy Cu 50% Ni 50% develops a very sharp cube texture and can be used as parent alloy for the development of ternary alloys.
In this aspect, a set of Cu-alloys (CuNiX) with 49,5wt% Cu, 49,5wt% Ni and 1w% of the alloying element of choice (Ge, Mo, Fe, Nb, Ta) were prepared to improve mechanical properties to the extent possible.
The tapes were obtained by cold rolling (deformation degree 98%) of the arc melted and homogenized (12 h, 800°C, atmosphere Ar/5%H2) starting alloy. After a two stage rolling (TSR) and two-step annealing (TSA) process the final texture was obtained. Using this novel process route a cube texture of >97% (tolerance angle 12%) was achieved for alloys with Nb.
Ternary CuNiNb alloy presents enhanced mechanical properties and have in the case of CuNiNb a yield strength of 135 MPa which is close to the requirement of 150MPa.
The qualification of the production process and enhancing the magnetic properties towards non-magnetic NiW substrates was an essential objective of the EUROTAPES project handled by EVICO.
Based on the technology developed at IFW 80 µm thick Ni7.5at%W and Ni9.0at%W metallic substrates up to lengths of 100 m were successfully manufactured. The main focus of the work was on optimization of the reel-to-reel (RTR) - production and annealing process to enable future industrial production. Optimized RTR texture annealing conditions resulted in reproducible high cube texture fractions of higher than 99 % for Ni7.5at%W and higher than 97 % for Ni9.0at%W representing very good results. This is a great progress in RTR-substrate processing, especially as with increasing W content the formation of grain boundary grooves is increased, the production process technology becomes more complex and process windows become very narrow.
The whole manufacturing process has been optimized regarding cost. As a result, the furnace temperature during the heat treatment could be lowered and the process time could be reduced by 30 min for a 100 m Ni9.0at5W tape by maintaining the same high texture quality of the tape. For an assumed demand of 100 km tape per year the reduced process time sums up to 500 h. These new production process parameters allow reducing cost by saving time and energy and leading to a higher efficiency of the process enabling an increase of production capacity.
In conclusion, the new Cu approach to substrate material for coated conductors made recognizable progress. The successfully manufactured non-magnetic Ni9.0at%W tapes with a length of 100 m were used for the production of a fully superconducting tape within the collaborations of the EUROTAPES project.
10. ENVIRONMENTAL ASSESSMENT OF SUPERCONDUCTING TAPES AND ROUND WIRE CONDUCTORS BY USING LIFE CYCLE ASSESSMENT (LCA) METHODOLOGY
In the framework of EUROTAPES project it was realised an environmental analysis of the different superconductor architectures developed and eligible to be scale-up at industrial scale. The main objective of this analysis was to calculate the potential environmental impacts associated to the production stage of these superconductor architectures. The environmental impacts of different production substages and processes involved were assessed, and main hotspots were identified. Besides this, alternative compositions, technologies, processes and methods developed within EUROTAPES project were evaluated and were compared with the current ones (or conventional), in order to determine the most environmentally friendly options and make final recommendations to reduce the environmental impact of superconducting architectures produced.
The methodology used to perform the environmental analysis was the Life Cycle Assessment (LCA) methodology. The scope of the analysis was defined as cradle-to-gate; that it means that for each architecture analysed, all the environmental impacts linked to the production stage were calculated, including the upstream processes (extraction and transformation of raw materials and production of energy used). Life cycle stages beyond the production of the final superconductors (transport, use and end-of-life) were excluded since they are out of the scope of the project and there is no available information. All the data used to calculate the environmental impacts of superconducting architectures was provided by project partners. When data was not available, data from literature or databases (GaBi and Ecoinvent) was used. All this data was introduced to LCA software (GaBi abd SimaPro) in order to calculate the environmental impact contributions of superconducting architectures on eight environmental impact categories: acidification, climate change, freshwater eutrophication, human toxicity, ozone depletion, photochemical ozone formation, water resource depletion, and mineral, fossil and renewable resource depletion.
Three different superconducting architectures were assessed:
1. Low cost superconducting tapes: NiW RABIT substrates architecture.
2. Medium cost superconducting tapes: SS substrate/ABAD-YSZ architectures.
3. Round wire conductors based on low cost superconducting tapes (hastelloy substrate architecture).
The results of the analysis on low cost superconducting tapes (NiW RABIT substrates) revealed that final protective coatings applied (silver coating and copper electroplating) have the highest environmental impact contributions, to the overall architecture. These environmental impacts are related to the extracting and obtaining processes of the raw materials used in the coating processes (copper oxide and silver) and also to the energy consumed during the copper electroplating process. The manufacturing of buffer and YBCO layers have high environmental impact contributions affecting the climate change and the ozone layer depletion, as a consequence of the energy consumed, solvents and precursors employed in the manufacturing processes of both layers.
In regards to medium cost superconducting tapes, two different production approaches (or routes) were assessed: the Pulsed Laser Deposition (PLD) route and the CSD (Chemical Solid Deposition) route. For the PLD route, the majority of environmental impacts are associated with the electrochemical polishing process, due to their high energy requirements, as well as to the final protective coatings, due to the raw materials used (as it has explained before). Concerning the CSD route, once again, final protective coatings (silver coating and copper electroplating) cause the main environmental impacts to the overall architecture. In addition to this, YBCO layer preparation contributes also with high environmental impacts in the ozone depletion as a consequence of the YBCO fluorinated precursors used.
Finally, the environmental analysis performed on round wire conductors based on low cost superconducting tapes concluded that main environmental impacts are related to the hastelloy substrate manufacture, especially to the nickel employed. Moreover, round wire process cause also remarkable environmental impacts as a consequence of the electricity consumed during the process. Last, the high thermal superconducting layer (GdBCO) production has also important environmental impacts, especially on climate change and ozone depletion, because of the use of Gadolinium, a rare earth element with a complex and selective obtaining process associated, which mobilises high flows of materials and energy.
As has mentioned before, alternative compositions, technologies, processes and methods were also evaluated and compared with the currently used, in order to determine the most environmentally friendly options. Results of this analysis reveal that in general, innovative processes developed or evolved thanks to EUROTAPES project have lower environmental impact contributions in comparison with conventional or currently used processes. The main highlights and recommendations proposed are:
- Results of the analysis conducted in the RABIT architecture confirmed that high W-alloyed Ni substrate (Ni9%W) has a better environmental profile than low W-alloyed Ni substrate (Ni5%W), achieving an environmental impact reduction about 10% in the substrate manufacturing substage, for all the eight impact categories studied. Therefore, the use of high W-alloyed substrates is particularly recommended.
- The LCA applied in this project proved that the innovative SDP process is more sustainable than the electrochemical polishing process. The application of SDP represents important environmental impact savings in the substrate preparation substage (between >99% to 61%) and for the overall architecture (between 8% to 58%). So as to decrease the overall environmental impacts of medium costs superconducting tapes, the application of SDP process instead of electrochemical polishing process to prepare SS substrates is recommended.
- The new metalorganic precursor solutions with low fluorine (low-F) content for YBCO layers are more environmentally friendly than conventional TFA solutions; it has been demonstrated a reduction of the environmental impacts of YBCO layer by 67%, for the ozone layer depletion, due to the lower generation of emissions of fluorinated compound into the atmosphere.
- An increase in tape's width to 40mm could reduce the environmental impacts associated to the production of medium cost superconducting tapes from 88% to 3%, depending on the impact category selected, so it has demonstrated to be an interesting proposal to reduce the environmental impact of superconducting tapes.
- On the other hand, IJP processes have reflected evident improvements in the energy consumption in comparison with other processes studied. Moreover, the promotion of energy efficiency strategies and/or the incorporation of energy supplied from renewable energy sources were determined as interesting actions to reduce the environmental impacts of template, buffer and HTS layers for the three architectures studied.
The EUROTAPES project has made evident their contributions to the improvement of superconducting technology in Europe and their commitment to environment and society, by developing new environmentally friendly solutions for the future of superconductivity industry.
Potential Impact:
High Temperature superconductors (HTS) are now very close of spreading power applications while they have also open new frontiers in the use of superconducting magnets. Coated conductors (CCs) have emerged as the best opportunity to enable a broad penetration of HTS on all power system and magnet applications. The main challenge of EUROTAPES was to be able to implement materials with novel nanostructures and reliable processing methodologies for long length CCs manufacturing, beyond 500 m in length, with a cost/performance ratio making them attractive for a wide market penetration.
EUROTAPES has made outstanding scientific and technological advancements providing definitive progress towards approaching the goal of achieving a low cost/performance ratio of CCs. The metrics to evaluate progress in the materials development and manufacturing capabilities, as well as capability for market penetration, need to be referred to the specific working conditions of the power systems and magnets intended for final use. Three different types of final use applications have been considered for the CCs leading to different working magnetic fields (low, high and ultra-high magnetic fields) and temperatures (77 K, ~30 K and 4.2 K, respectively). The techno-economic metrics are then defined for each of these working conditions. For instance, for applications at 77 K and self-field (cables, FCL, transformers) the required cost/performance ratio is ~100€/kA m for 1 m of conductor and 1 cm wide. Instead, costs below this value can be achieved at 4.2 K under a magnetic field of 30 T (ultra-high field magnets).
The EUROTAPES project defined a twofold strategy. First, to develop novel advancements which decrease the CCs manufacturing cost. The paths to follow were: simplified conductor architectures and less costly methodologies implemented in long length manufacturing processes with a high throughput and high yield. The second goal was to enhance the superconducting performance of the CCs under the working conditions of the different applications, i.e. mainly to enhance the total critical current Ic (H, T) of the conductors under magnetic field.
The deployed research activities have boosted the European industry of superconducting materials towards a worldwide competitive position for HTS power systems and magnet development. This is reflected in many new initiatives at industrial and R&D levels in Europe where the EUROTAPES partners are involved.
The impact of HTS in achieving the EU vision of a smart and sustainable electrical grid with a high percentage of renewable sources is very high. Electrical power technologies based on HTS have a strong potential for improved efficiency in generation (wind generators) and transmission, as well as in enhancing power grid stability. Transport applications (aeronautics, ship propulsion) may also benefit of these developments. The unique properties of HTS key for these achievements are: 1/ Low losses in ac and dc power systems (cables, transformers, motors, Fault current limiters); 2/ Increased power density and simplified engineered systems, lighter and smaller equipment (generators/motors); 3/ Fast impedance transitions allowing to reach an enhanced grid stability (FCL); 4/ High energy and power densities for electromagnetic energy storage (SMES).
The impact of HTS conductors in scientific and biomedical applications requiring high magnetic fields will be as well huge. The future of large scientific installations, using accelerators (CERN) or fusion installations (ITER), will make extensive use of the unique HTS magnet capabilities. The mid-term technological strategies in these areas are closely determined by the availability of HTS conductors and cables. Finally, the large demand of superconductors for medical and biochemical applications (MRI, NMR, compact accelerators for hadron radiotherapy) will also widely benefit of making available a new series of high and ultra-high magnetic field HTS conductors.
Main dissemination activities and the exploitation of results
Dissemination activities
EUROTAPES project has had a significant impact on the scientific community thanks to its excellent results but also on the European society being its citizens that can be defined as the “public” in this case. Therefore, efforts have been made to inform the general public directly mostly through digital channels and indirectly through the media that contribute largely to a wide diffusion of the news.
The objective of the communication concentrated on the general public is to show them that superconductivity is essential for Europe for various aspects as it has a direct impact on many economic sectors (renewable energies, electricity networks, astrophysics, competitively, environment and more) and that European research is delivering excellent and concrete results.
Target audience: It includes amongst others the scientific and academic community, the industry and end users, and public administration and regulatory authorities.
Main actions of public awareness
Various actions were undertaken to ensure an effective public awareness: direct and indirect ones.
The direct ones are defined as news items published on the project’s website (or of the partners) with the objective that the public will read it directly without being digested by external persons. The advantage is that there is a full control over the content that is being published. However, the amount of views and the outreach of the news item is limited. The audience will reach the webpage either because they know the website and they want to follow the news of the project or of the organisation, or because the search engine they use will bring them to this page because the key words correspond to the news item. In any case, the outreach is limited as the EUROTAPES website has on average around 10 visits per day.
The indirect actions are the ones with the help of external persons such as journalists. The news item is being sent to journalists and according to their interest, the importance of the news item and the moment, they make a news item out of it by mixing it often with other sources. The outreach of these indirect actions is much bigger than of the direct ones although the inconvenient is that the consortium cannot control what is being published. However, this is necessary so journalists can cross information and compare facts in order to inform their readers. Nevertheless, from experience, the content published by the media was quite accurate and close to the facts. Therefore, the consortium was very glad to benefit from visibility with the help of the media.
Three main actions were done during the project to raise public awareness around the project:
a. Websites publications
On the EUROTAPES website, 36 news items were published during the lifetime of the project, which corresponds to a more than one item every two months. As said, on average, the website has around 10 visits per day since the analytics service was installed (November 2013). In total, it benefited from 19’000 visits. A peak of 202 visits in one day was reached when the press conference was organised at the end of the project (15th of March 2017).
b. Press release
On the 17th of May 2016, one year before the end of the project, the consortium issued a first press release that was distributed to various media organisations in Europe with the help of a large news agency (Business Wire). The content was elaborated by the coordinator and the communication manager with the approval of the consortium.
A total of 19’506 views has been reached according to the statistics of the news agency although the large part of these views were made during the first 24 hours after publishing the news item.
It was translated from English into German, French, Dutch, Italian and Spanish in order to better reach the media. This press release was crucial to start informing the press and the public about the existence of EUROTAPES and its impact in the scientific environment and on the economy. The impact was quite successful and it was a good preparation for the second and final press release and conference.
c. Press conference
At the very end of the project with the results clearly defined, the major event of public awareness was organised in Barcelona between the ICMAB, Oxolutia and LEITAT with the strong support of the representation of the European Commission in Barcelona and its media team from DG COMM. On the 14th of March 2017, Prof. Xavier Obradors, Prof. Teresa Puig, Dr. Albert Calleja presented EUROTAPES during a press conference (accompanied by a press release) in Barcelona in the representation of the European Commission in Barcelona. Around 15 journalists attended, 3 additional interviews for radio and TV were made and many news articles were published in international media.
A dissemination leaflet has been done and is available on the EUROTAPES website. In the leaflet, the EUROTAPES technical information have been synthesized for a better comprehension of the general public. It has been updated and distributed to all partners and all stakeholders met during the project during events, meetings and conference. An updated version has been released in the last period of the project.
Scientific Dissemination
The main objective of the Scientific Dissemination is to spread the knowledge to the Scientific Community, within EUROTAPES consortium the following activities have been performed.
99 Scientific publications
299 Dissemination activities including, Oral presentations, Poster, Workshop, participation in conferences, articles.
Exploitation of the results
Regarding the exploitation activities, in order to ensure that the R&D developments of a project have an impact, it requires not only the obvious research development but also the analysis from a market point of view, in order to map the project outcomes onto the actual market needs and realities
Eight Key Exploitable Results (KERs) have been identified and a strategy of exploitation has been proposed and it will be carried out by the partners, owners of these technologies jointly with other partners that have interest in using these results. A brief summary of the technology analysis is provided below:
The first KER (KER n°1) is the Ink Jet Printed planarization layers of metallic substrates. It is the amorphous oxide layers deposited by the Chemical Solution Deposition technique (SDP, Solution Deposition Planarization) on metallic substrates for IBAD or ABAD template deposition. This can be accomplished by inkjet printing deposition in reel-to-reel configuration at tape speeds of 40 m/h approx. The surface imperfections like scratches, pores or protuberances are covered and filled with the ink, which becomes a solid planarization layer upon suitable thermal treatments.
The second KER (KER n°2) is Metal Oxide Nanoparticles stabilized in alcoholic media. More precisely, these are Stable Alcoholic Colloidal Solutions of Metal Oxide nanoparticles prepared using the polyol synthesis by Thermal, Microwave(MW) and/or Solvothermal activation approaches. Our unified methodology offers stable mono (CeO2, ZrO2) and binary metal oxide (MFe2O4, M=Fe, Co,Mn and BaMO3, M=Ti, Zr, Hf), colloid solutions with a high size control and narrow dispersion in a broad range of concentrations (up to 0.2M) in alcoholic solvents.
The third KER (KER n°3) is called Low fluorine metal organic solutions for Ink Jet Deposition of superconducting layers. Briefly explained, this entails novel compositions of inks with metalorganic precursor solutions of Y, Ba and Cu with a strong reduction of the F content and additives and solvents which are adapted to IJP deposition of homogeneous thick films in continuous mode using piezoelectric heads.
The fourth KER (KER n°4) are conductors on round core cable. These are round wire made of HTS tapes wound helically on metallic tube and covered by polymeric foam that insulates thermally and contains a cooling channel.
The fifth KER (KER n°5) are Advanced (non-magnetic cube textured) Cu-based metallic substrates. In entails the production of nonmagnetic cube metallic substrate with recycled copper, reducing raw material cost and energy.
The sixth KER (KER n°6) is the Ink Jet Printing reel-to-reel pilot plant. Continuous production of thin films from chemical solutions has been materialized in a reel-to-reel pilot plant including ink jet printing as deposition method.
The seventh KER (KER n°7) is the Advanced Magnetoscan system for quality control of coated conductors. The measurement of the critical current of coated conductor tapes is most important for quality control and has to be done with every tape.
The eighth KER (KER n°8) are absolutely straight, non-magnetic and at the same time highly cube textured Nickel-Tungsten-based metallic substrate tapes for coated conductor production.
Taking all this into consideration, we can conclude from one side that all the channels used to disseminate the projects have achieved the expected impact and that all the consortium has contributed to it. From the other side, the project has finished with eight exploitable results that have a potential market within the superconducting sector, there is an exploitable plan set for each result individually and for EUROTAPES as a whole and the partners involved are committed to continue their exploitation activities beyond the project.
List of Websites:
http://eurotapes.eu/
Project Coordinator
Prof. Xavier OBRADORS
AGENCIA ESTATAL CONSEJO SUPERIOR DE INVESTIGACIONES CIENTIFICAS
xavier.obradors@icmab.es
