Symposium Organizers
Paolo Mele, Muroran Institute of Technology and Shibaura Institute of Technology
Jens Haenisch, Karlsruhe Institute of Technology
Eric Hellstrom, Applied Superconductivity Center FAMU-FSU College of Engineering
Takanobu Kiss, Kyushu University
Symposium Support
Advanced Conductor Technologies
Research Institute of Superconductor Science and Systems, Kyushu University
Shanghai Creative Superconductor Technologies Co., Ltd.
Siemens AG, Corporate Technology
Supercoil Co., Ltd.
SuperOx Japan LLC, Sagamihara Incubation Center (SIC-3)
EN03.01: REBCO Coated Conductors—Industrial Manufacturers
Session Chairs
Paolo Mele
Xavier Obradors
Tuesday PM, April 03, 2018
PCC North, 100 Level, Room 125 B
10:30 AM - EN03.01.01
Materials, Technical and Economic Aspects of Development, Up-Scaling and Application of 2G HTS Wires by IBAD/PLD Approach
Sergey Lee1
SuperOx Japan1
Show AbstractSince the discovery of high temperature superconductivity (HTS) the most advanced materials of top performance in this field are so-called superconducting tapes of the second generation (2G-HTS) – the new class of 2D nanomaterials consisting of several multilayers with precisely controlled chemical composition, structure and grain orientation within the scale of hundreds meters length. Manufacturing of long-length 2G-HTS tapes is extremely challenging from the materials point of view. Combination of most advanced sputtering techniques including ion-beam assisted deposition (IBAD) and pulsed laser deposition (PLD) methods has proved to be one of the most reliable and promising technique.
At present several companies including Fujikura, Bruker, Shanghai Superconductors and SuperOx routinely produce tens of kilometers of high performance 2G HTS tapes, however further prospects for up-scaling IBAD/PLD approach towards manufacturing of hundreds and thousands of kilometers of tapes is not clear yet. It depends on the several factors including overall situation on the superconducting market, which closely related with the price of cooling equipment and superconducting materials. In this presentation I am are considering IBAD/PLD upscaling from the viewpoint of recent progress in sputtering and laser technologies and the latest results in 2G wire production and designing of deposition equipment made in past 5 years by our company.
Since 2012 SuperOx group produced and delivered several tens of kilometers of superconducting tapes with high degree of customization for R&D and commercial projects worldwide. I will give a brief overview of main results obtained during past few years since the establishment of SuperOx Japan and describe our company strategy and vision on future development of 2G HTS wires production and applications.
In 2016 we made a substantial progress in up-scaling of our production and installation of independent new high-throughput equipment in Japan and Russia. Currently SuperOx activity for upgrading of manufacturing facilities aimed to increase the production throughput and yield and to improve the performance of 2G HTS wires with a wider range of customization of our product tapes. Based on our recent cost analysis model I will discuss the potential pathways to reduce the final price of our wires, which based on the magnetron-IBAD-PLD production scheme and discuss the main problems and obstacles of this approach in comparison with other techniques.
SuperOx involved in several R&D and commercial projects including development of advanced superconducting fault current limiters, cables, current leads, induction heaters, motors etc. In conclusion, I will present a brief overview of our ongoing and prospective projects aimed on the development of new materials, wire architectures, construction of pilot scale devices and electrical equipment.
11:00 AM - EN03.01.02
Industrialization Progress of HTS 2G Wire in SuNAM
Seung-Hyun Moon1
SuNAM Co Ltd1
Show AbstractSuNAM has been producing long-length coated conductors based on a proprietary process which consists of electron beam co-evaporation of constituent metals and subsequent conversion of precursor film to superconducting phase by carefully controlling temperature and oxygen pressure. After securing stable manufacturing routine for upto 1 km-long wires, with about 10 percent uniformity in critical current enabled by various quality control measures, we tried to further increase critical current above 1,000 A/cm-width. This goal should be achieved by increasing thickness of superconducting layer while retaining critical current density, or even enhancing it. We varied co-evaporation process to enhance composition uniformity, and also modify temperature and pressure profile in heat treatment furnace to better utilize conversion dynamics of GdBa2Cu3O7-x phase formation, and the results will be presented.
With these wire, we made 400 mH compact reactor with cryogen free operation. The reactor’s operating current is over 1,500 A at temperature is around 10 K. Detailed design, construction, and operating results will be discussed. And first all HTS CC base commercial 18 T magnet result will be introduced. A 70 mm cold bore high temperature superconducting (HTS) magnet was developed for axion detector system of Center for Axion and Precision Physics (CAPP) research center in Institute for Basic Science (IBS) in the Republic of Korea. A key parameter for axion detector magnet is to generate high and longitudinally uniform magnetic field in RF cavity. Magnetic field strength on -100 mm < z < 100 mm in coil bore space should be larger than 90 % of it at magnet center.
Finally we’ll summarize a commercialization & industrialization efforts in Korea, and suggest a key issues to open the true market.
11:30 AM - EN03.01.03
Development of BMO-REBCO Coated Conductor by Hot-Wall PLD Process on IBAD Template
Yasuhiro Iijima1
Fujikura Ltd1
Show AbstractDuring the past 25 years, worldwide R&D efforts were concentrated on development of REBCO coated conductor (C.C.), which was expected to have the strongest pinning properties in wide temperature/field range. The in-field performance for REBCO conductors still have growth potential by using artificial pinning centers (APC), as BMO doping technology with nanometer size rod-like structure, etc. But it was a tough challenge to get end-to-end uniformity even for non-APC REBCO conductors, because c.c. is essentially characterized as reel-to-reel sequential process for single-crystalline-like triaxially textured films on flexible metal substrate, where it is still the only way to avoid intergrain weaklinks for REBCO wires.
In order to obtain good longitudinal Ic homogeneity of c.c., we had chosen hot-wall type pulsed-laser-deposition (PLD), which realized quite homogeneous crystalline growth conditions for REBCO deposition by furnace-like, nearly equilibrium substrate heating, on sharply textured buffer layers formed by using large-area ion-beam- assisted-deposition (IBAD). As a results, reliable production line of homogeneous non-doped REBCO tapes with lengths over 500 m had been developed with typical Ic performances over 500 A/cm at 77 K in the self-field and over 1000 A/cm (Jc=5-6 MA/cm2) at 30 K in 2 T. Recent years we applied the process for introduction of rod-like APC as BaMO3 (BMO, M : Zr or Hf) -doped REBCO conductors and found a productive process condition of BMO-doped high-performance tapes with good longitudinal homogeneity. 300-600m long class uniform BaHfO doped EuBCO tapes were formed with productive high growth rate of 20-30 nm/sec, being faster than commercial non-doped conductors, which had also large Ic of 1700-2000A/cm (Jc=7-8 MA/cm2) at 30K, 2T. The angular dependence of in-field Jc properties were investigated in wide temperature range, and strongly c-axis correlated flux pinning were observed over 30K, especially in those films with the growth rate limited lower than 5 nm/sec, where the minimum values of Jc were not so different from high growth rate over 20 nm/sec. These results indicate reliable controllability of deposition parameters on high-rate APC introduction by using hot-wall PLD process. Ic homogeneity analysis of long-length BMO-REBCO c.c. and the microstructural analysis for the growth of BMO rod-structure would be discussed correlated with growth speed, BMO composition, etc.
This Paper includes the results supported by the New Energy and Industrial Technology Development Organization (NEDO).
EN03.02: REBCO Coated Conductors—Processing Studies and Applications
Session Chairs
Tuesday PM, April 03, 2018
PCC North, 100 Level, Room 125 B
2:00 PM - EN03.02.01
Recent Development Progress of Superconducting Induction Heater with Superconducting Magnets in Korea
Jongho Choi1,Sangho Cho1,Minwon Park2
Supercoil1,Changwon National University2
Show AbstractLarge-scaled induction furnaces for non-ferrous metal billets operated at commercial frequency have an energy efficiency of only 50~60% due to the considerable loss from the copper coils used to generate the magnetic fields. Efforts to improve their efficiency are hampered by physical limits. A DC induction heating using HTS magnets has been suggested for achieving higher energy efficiency.
A 10kW-class prototype for an HTS DC induction heater was developed in 2013. Changwon National University and TECHSTEEL had completed a project to develop a 300 kW-class superconducting induction heater(SIH) with HTS magnets in 2017. And Supercoil Co., Ltd., which had established on Sep. in 2016 as a professional development company of the SIH and superconducting magnet, initiated the business of the SIH since 2017.
In this paper, we are going to introduce a 300 kW-class SIH and its performance test results. The HTS magnets were fabricated and excited under the conduction cooling condition, successfully. Now, the SIH with the HTS magnets are being fabricated and tested to heat up the metal billets including both the ferrous and non-ferrous metal billets. The MgB2 magnet was developed for the SIH, too. The performance test results will be presented, in detailed. The all performance test results will be applied for the commercial product of SIH.
3:30 PM - EN03.02.03
Progress in High Critical Current Nanocomposite YBa2Cu3O7-x Coated Conductors from Colloidal Solutions
Xavier Obradors1,Teresa Puig1,Ziliang Li1,Cornelia Pop1,Natalia Chamorro2,Bohores Villarejo1,Flavio Pino1,Ferran Valles1,Bernat Mundet1,Laia Soler1,Julia Jareño1,Silvia Rasi1,3,Juri Banchewski1,Roger Guzman1,Jaume Gázquez1,Mariona Coll1,Anna Palau1,Susagna Ricart1,Josep Ros2,Jordi Farjas3,Pere Roura3
ICMAB - CSIC1,UAB2,Univ. Girona3
Show AbstractHigh current superconducting wires for large scale power applications and magnets has been one of the most challenging achievements during all the HTS era which encompasses many materials science and engineering challenges. Coated conductors of YBa2Cu3O7 (YBCO) have emerged as the most attractive opportunity to reach unique performances while reducing the cost/performance ratio continues to be a key objective at present. Chemical solution deposition (CSD) is a very competitive cost-effective technique which has been used to obtain nanocomposite films and CCs. In the recent years we have been able to demonstrate the unique potentiality of CSD techniques based on Ink Jet Printing deposition to achieve low cost, low anisotropy and high critical current coated conductors. In this presentation, we will report on recent progress on the development of growth process and enhanced vortex pinning of CSD nanocomposite YBCO films, obtained from colloidal solutions where preformed oxide nanoparticles (NPs) stabilized in the YBCO precursor solutions are used. A thorough investigation correlating the pinning landscape with the defect microstructure has been pursuit through detailed angular dependent in-field critical currents and HRTEM/STEM analysis. We will also report how CSD nanocomposites can be obtained through a new approach based on a transient-liquid assisted growth (TLAG) enabling ultrafast growth rates in the range of 50 nm/s.
4:00 PM - EN03.02.04
Ultrafast Growth of Epitaxial YBCO Films by Transient Liquid Assisted Growth
Silvia Rasi1,Julia Jareño2,Laia Soler2,Juri Banchewski2,Roger Guzman2,Susagna Ricart2,Jordi Farjas1,Pere Roura1,Cristian Mocuta3,Xavier Obradors2,Teresa Puig2
University of Girona1,ICMAB, Institut de Ciencia de Materials de Barcelona (CSIC)2,Synchrotron SOLEIL3
Show AbstractNowadays, the application of high temperature superconducting tapes for energy transport and electrical power devices is limited by its production cost. Therefore, it is of the utmost importance to develop a cost-effective synthetic route of high-throughput YBa2Cu3O7 (YBCO) film growth. Chemical solution deposition of metal organic precursors (CSD-MOD) is known to be a good candidate to fulfil this challenge. YBCO growth rates for the traditional route based on fluorinated precursors are limited by the very low HF out-diffusion during BaF2 decomposition.
On the other hand, Y2O3 diffusion through BaO-CuO melts is known to be very high, thus enabling high growth rates. We propose a CSD route using fluorine free (FF) precursors that, upon proper decomposition of BaCO3, follows the formation of a transient liquid that results from the eutectic reaction between BaO and CuO. The YBCO layers obtained from this Transient Liquid Assisted Growth (TLAG) method achieve epitaxial films with superconducting transition temperatures of 90 K and critical current densities at 77 K of 3 MA/cm2.
In this communication, we present two different methods to grow YBCO with the desired c-axis orientation: the temperature-step route and the PO2-step route. In the first case, very high heating rates (20-60 °C/s) at a constant pressure force the system to reach the correct region of the phase diagram for the epitaxial growth, and where the precursors (BaCO3) are fully decomposed. By contrast, in the second route, precursor decomposition and YBCO growth are decoupled, by decomposing BaCO3 at low PO2 (~10-6/10-7 bar) where YBCO growth is prevented. Afterwards, an increase of O2 partial pressure results in YBCO epitaxial growth. To understand the growth process and reaction paths, advanced high-resolution Scanning Transmission Electron Microscopy (STEM), In-situ x-ray diffraction, and synchrotron radiation have been employed. Growth rates between 25 and 50 nm/s have been achieved.
Finally, we will also show the compatibility of the TLAG process with the growth of nanocomposites using preformed nanoparticles of BaZrO3.
Acknowledgements
This work was partially funded by MINECO (project MAT2014-51778-C2); Generalitat de Catalunya (contract 2014SGR-00948); Universitat de Girona (contract MPCUdG2016/059); Center of Excellence award Severo Ochoa (SEV-2015-0496) and ERC-2014-ADG-669504-ULTRASUPERTAPE
4:15 PM - EN03.02.05
Development of Low-Fluorine Solution Route and DUV Photolysis Process for YBa2Cu3O7-x Coated Conductors
Yuanqing Chen1,2,Weibai Bian1,Lingwei Li1,Yang Song1,2,Aditya Yerramilli2,N. David Theodore2,3,Terry Alford2
Xi'an University of Technology1,Arizona State University2,NXP Semiconductors3
Show AbstractIn this study, a low-fluorine solution route was developed for the fabrication of YBa2Cu3O7-x(YBCO) coated conductors. In this approach, the solution contains 20-30% of the fluorine of the traditional all-trifluoroacetate solution route. This enables high-speed production of much smoother YBCO films. We systematically investigated the influence of the fluorine content on the phase evolution and superconducting properties of the films. We found that a broad range of fluorine contents can be used to prepare thin high-quality YBCO films. In contrast, for thick YBCO films (with thicknesses over 1μm), F/Ba=2 (in the solution) is optimal to obtain high-Jc YBCO films. So, we used a solution with F/Ba=2. We also developed a deep UV light soaking technique to prepare YBCO films. Instead of thermal pyrolysis of the precursor film, we used UV light to decompose the precursor. This resulted in the constituent elements being uniformly distributed in the films, resulting in enhanced Jc. The addition of water vapor (during the UV irradiation) resulted in the formation of radical O*. This promoted the removal of carbon residue from the films, and further increased the Jc of the resulting YBCO films.
4:30 PM - EN03.02.06
Progress Towards YBa2Cu3O7-δ Nanocomposite Thin Films Using Low-Fluorine Chemical Solution Deposition and Preformed Nanocrystals
Klaartje De Buysser1,Hannes Rijckaert1,Hänisch Jens2,Max Sieger3,Ruben Hühne3,Jonathan De Roo1,Petriina Paturi4,Hannu Huhtinen4,Jan Bennewitz5,Katrien De Keukeleere1,Michael Bäcker6,Isabel Van Driessche1
Ghent University1,Karlsrhue Institute of Technology2,IFW Dresden3,University of Turku4,BASF SE5,Deutsche Nanoschicht6
Show AbstractThe implementation of YBa2Cu3O7-δ (YBCO) coated conductors in power applications generally has a potential to change the paradigm in large-scale energy applications. Unfortunately, pure YBCO thin films typically exhibit a strong reduction of the critical current density (Jc) with increasing magnetic field strength caused by vortex motion. There are many different synthetic strategies available to produce superconducting YBCO thin films, of which many are not commercially viable. Here, we collaborated with companies in the field, choosing the approach that will be used for production. It is based on chemical solution deposition (CSD) of a precursor solution with several fluorine contents.
Hereby, the incorporation of preformed nanocrystals (PNCs) as artificial pinning centers was introduced as an adequate approach to achieve flux pinning, preventing the drastic decrease of the critical current density Jc at moderate-to-high magnetic fields as well as its angular dependency on the magnetic field. To achieve this, we have produced nanocomposite thin films starting from PNCs in combination with fluorine-based chemical solution deposition. The use of PNCs generally offers a better control of the final microstructural properties of the nanocomposite films when compared to self-assembled nanoparticles formation during YBCO processing.
In this work, small crystalline single (ZrO2 and HfO2) and double (SrTiO3 and BaZrO3) metal oxide nanocrystals were synthesized with diameters in the range of 4-10 and capped with hydrophobic ligands to ensure colloidal stability in apolar solvents. However, as the YBCO precursor typically provides a more polar environment, e.g., methanol, an important aspect of this research involves ligand exchange and the appropriate stabilization procedure. We are able to stabilize these nanocrystals in different types of fluorine-based YBCO precursor solutions, leading to highly stable nanocomposite precursors with long shelf-lives.
Afterwards, the YBCO-PNC solutions were deposited on single crystal LaAlO3 (LAO) substrates via ink-jet printing method. The main focus of this research pointed to understanding the factors which control the microstructure development and the physical properties of the nanocomposite thin films. By strict optimization on both the precursor and processing level, we achieved nanocomposite thin films exhibiting Jc of 4-5 MA/cm2 at 77 K in self-field as well as a much smoother decay of Jc as a function of magnetic field. This is reflected by a strong pinning force enhancement (up to 17 GN/m3 at 77 K) and a reduced effective anisotropy compared to undoped YBCO films.
This newly developed approach delivers scalable and high quality superconducting films, capable of meeting the strict requirements for the successful implementation and distribution of coated conductors throughout energy market.
4:45 PM - EN03.02.07
Thick-Film REBCO Coated Conductor by Advanced Metal Organic Chemical Vapor Deposition
Rudra Pratap1,Goran Majkic1,Eduard Galstyan1,Mehdi Kochat1,Vasish Mohan1,Venkat Selvamanickam1
University of Houston1
Show AbstractWe report the development of high performance thick (Gd,Y)Ba2Cu3Ox tapes in a single pass using an Advanced Metal Organic Chemical Vapor Deposition (A-MOCVD) system. Record high critical current (Ic) of over 7200 A/cm at 30 K, 3 T (BIIc) has been achieved in heavily doped (15 mol. % Zr addition), 4.8 µm (Gd,Y)Ba2Cu3Ox tapes with a record high lift factor of ~11. This corresponds to an extremely high engineering current density (Je) of over 7000 A/mm2.
In addition, Ic of over 2100 A/4 mm at 4.2 K, 14 T (BIIc) has been achieved in heavily doped (15 mol. % Zr addition), 4.3 µm (Gd,Y)Ba2Cu3Ox tapes on IBAD- MgO/LMO substrates .It corresponds to a pinning force (Fp ) of 1.7 TN/m3 and an record engineering current density (Je) of over 5100 A/mm2 which is almost double of the highest value ever reported.
We attribute this achievement to excellent temperature control and laminar flow feasible in A-MOCVD, coupled with optimization of BaZrO3 nanocolumn growth parameters. High density of BaZrO3 nanocolumns of average size 4-5 nm and an average spacing of 18-19 nm between them contributes to superior flux pinning properties.
This work is supported by the Department of Energy Advanced Manufacturing Office and the Office of High Energy Physics.
Symposium Organizers
Paolo Mele, Muroran Institute of Technology and Shibaura Institute of Technology
Jens Haenisch, Karlsruhe Institute of Technology
Eric Hellstrom, Applied Superconductivity Center FAMU-FSU College of Engineering
Takanobu Kiss, Kyushu University
Symposium Support
Advanced Conductor Technologies
Research Institute of Superconductor Science and Systems, Kyushu University
Shanghai Creative Superconductor Technologies Co., Ltd.
Siemens AG, Corporate Technology
Supercoil Co., Ltd.
SuperOx Japan LLC, Sagamihara Incubation Center (SIC-3)
EN03.03: Studies of Granularity and Defects in HTS
Session Chairs
José Lorenzana
Jun-ichi Shimoyama
Wednesday AM, April 04, 2018
PCC North, 100 Level, Room 125 B
8:30 AM - EN03.03.01
Granularity Effects in Cuprate, Iron-Based, and MgB2 Superconductors
Michael Eisterer1
TU Wien1
Show AbstractTechnical conductors are inherently polycrystalline and do not behave as a single crystal in most cases. In MgB2 wires, the changing crystallographic orientation of the grains leads, together with the upper critical field anisotropy of this material, to a variation of the local properties when a magnetic field is applied. In the cuprate superconductors on the other hand, this effect is negligible compared to a grain-to-grain misalignment, which drastically reduces the critical current. The strategy for overcoming this limitation was the development of highly textured conductors, most successfully by the coated conductor technology. However, granularity effects are still relevant in some architectures. The grain boundary limitation is weaker in the iron-based superconductors, which may enable cheaper production techniques.
Recent scanning Hall probe measurements are reported addressing granularity effects in different superconductors. While granularity effects can be directly visualized for two-dimensional films, average inter- and intra-granular currents can be obtained from bulk samples. Strategies for optimization of granular materials will be discussed.
9:00 AM - EN03.03.02
Atomic-Scale Investigation of Interface Effects in Two-Dimensionally Doped La2CuO4 and La2CuO4/ La2-xSrxNiO4 Superlattices
Yi Wang1,Y. E. Suyolcu1,Wilfried Sigle1,Ute Salzberger1,F. Baiutti1,G. Gregori1,G. Christiani1,G. Logvenov1,J. Maier1,Peter van Aken1
Max Planck Institute for Solid State Research1
Show AbstractPhysical phenomena at interfaces of complex oxide hetero-structures have stimulated intense research activities due to the occurrence of a broad range of electric and magnetic functionalities that do not pertain to the constituting single phases alone. Interface effects have been proven to be a powerful tool for improving or even inducing novel functionalities [1, 2]. In the case of interface superconductivity, the interatomic structure relaxation and charge transfer play a key role. In this work, we combine atomic-resolved quantitative STEM imaging with analytical STEM-EELS/EDX analysis to investigate interface effects in La2CuO4 (LCO)-based hetero-structures, i.e. superlattices of two-dimensionally (2D) Sr-doped LCO and LCO/La2-xSrxNiO4 (LSNO) hetero-structures, both exhibiting Tc up to 40 K, despite its non-superconducting constituents. We lay emphasis on detailed and quantitative STEM analysis to understand the interplay between interface effects (cation and electron hole redistribution, as well as local lattice and oxygen octahedral distortion) and high-temperature interfacial superconductivity.
With atomically resolved EDXS and EELS analyses, we investigate the cation intermixing, i.e. La/Sr and Ni/Cu, at the interface of superlattices. Oxygen K-edge fine structure analysis were used to quantify the electron hole population. The electron hole profile reveals that charge redistribution occurs at the interface. Atomic-resolved high-angle annular dark-field (HAADF) and annular bright-field (ABF) images, which were simultaneously acquired, were used to evaluate the local lattice and copper-apical-oxygen distortions at these interfaces. The interatomic structure analysis shows that the copper-apical-oxygen distance has a remarkable variation near the interface [3]. We observe an anomalous expansion of the apical oxygen–oxygen distance at the downward side of the interface, and a substantial shrinkage of the apical oxygen–oxygen distance on the upward side in the growth direction of the thin film. Finally, the correlation of these results with the observed Tc will be discussed.
References:
[1] A.Gozar et al., Nature 455 (2008), p.782.
[2] F.Baiutti et al., Nat. Commun. 6 (2015), p. 8586.
[3] Y.Wang et al., ACS Appl. Mater. Interfaces. 8 (2016) p. 6763
9:15 AM - EN03.03.03
Atomic-Scale Probing of Oxygen Vacancies and Associated Distortions in YBCO
Bernat Mundet1,Jaume Gázquez1,Roger Guzman1,Steven Hartman2,Guangfu Luo2,Rohan Mishra2,Elena Bartolome3,Mariona Coll1,Anna Palau1,Teresa Puig1,Xavier Obradors1
Institute of Material Science of Barcelona (ICMAB)1,Washington University in St. Louis2,Escola Universitària Salesiana de Sarrià (EUSS)3
Show AbstractControlling the oxygen content (δ) is a key issue in the fabrication of YBa2Cu3O7-δ (YBCO) films since subtle variations in δ lead to large structural distortions and alter the number of available carriers within the superconducting CuO2 planes, which ultimately affect the superconducting properties [1]. It is commonly accepted that oxygen vacancies are located within the CuO-chains; however, in this talk, we will present results challenging this hypothesis. We have used aberration-corrected scanning transmission electron microscopy (STEM) to show a periodic and uneven distribution of Oxygen vacancies located at the BaO planes, especially in the proximity of Y2Ba4Cu8-γO16-d (Y124) intergrowths, the most common defect in YBCO. The presence of these Oxygen vacancies triggers structural changes in the superconducting planes reducing the symmetries of the YBa2Cu3O7-x unit cell: the Oapical-Cu spacing increases as well as the O-Cu-O angle of the CuO2 planes. Our results are supported by first-principles density-functional theory calculations, which show comparable formation energy of oxygen vacancies in Cu-O chains and in Ba-O planes. Additionally, previous results showed that Y248 intergrowths comes along with Cu and Oxygen vacancies buried within the very same planar defect, which in turn induce a dilute ferromagnetism in the superconducting state of the YBCO [2]. We will discuss the implications of all the observed distortions on the YBCO superconducting properties.
[1] Jorgensen J D, Veal B W, Paulikas A P, Nowicki L J, Crabtree G W, Claus H and Kwok W K 1990 Structural properties of oxygen-deficient YBa2Cu3O7- Phys. Rev. B 41 1863–77
[2] Gazquez J, Guzman R, Mishra R, Bartolomé E, Salafranca J, Magén C, Varela M, Coll M, Palau A, Valvidares S M, Gargiani P, Pellegrin E, Herrero-Martin J, Pennycook S J, Pantelides S T, Puig T and Obradors X 2016 Emerging Diluted Ferromagnetism in High- T c Superconductors Driven by Point Defect Clusters Adv. Sci. 3 1500295
Authors acknowledge the MICIN (NANOSELECT, CSD2007-00041 and MAT2014-51778-C2-1-R), Generalitat de Catalunya (2014SGR 753 and Xarmae), and the EU (EU-FP7 NMP-LA-2012-280432 EUROTAPES project, Cost Action MP1201 and CA16218 NANOCOHYBRI). They also acknowledge MINECO for the Center of Excellence award Severo Ochoa (SEV-2015-0496).
9:30 AM - EN03.03.04
Hybrid Microscopy of IMD Processed MgB2 Round Wires—Combination with X-Ray Tomography and Scanning Hall Probe Microscopy
Kohei Higashikawa1,Takanobu Kiss1,Shuhei Bouchi1,Masayoshi Inoue1,Hiroaki Kumakura2,Dongliang Wang3,Yanwei Ma3
Kyushu University1,NIMS2,IEE CAS3
Show AbstractCombining X-ray tomography and in-field scanning Hall probe microscopy (SHPM), we have succeeded in visualizing local distortion of filaments in IMD processed-MgB2 wires and their influence on critical current distribution in the MgB2 wires. High resolution X-ray tomography is a powerful tool to investigate filamentary architecture and local distortion such as sausaging effect and exudation of Mg. From the magnetic image of the magnetized MgB2 wire measured by the SHPM, we could evaluate spatial distribution of local critical current density, Jc, according to Biot-Savart law. The in-field SHPM allows us to evaluate critical currents quantitatively of the MgB2 wire with magnetic sheath materials by the measurement where the external magnetic field is higher than the saturation field of the magnetic sheath [1]. The advantage of such magnetic measurements is also to evaluate high current region in which transport method is difficult to apply. Combination with the X-ray tomography and the SHPM leads abundant information on current limiting mechanism of the MgB2 wires by synergistic effect.
[1] K. Higashikawa et al., IEEE Trans. Appl. Supercond. 26 (2016) 6200804.
Acknowledgements: This study was supported by Japan Science and Technology Agency (JST) as ALCA and also by by Japan Society for the Promotion of Science (JSPS) and Chinese Academy of Sciences (CAS) under the Japan – China Research Cooperative Program.
EN03.04: Physics of HTS Materials
Session Chairs
Michael Eisterer
Kohei Higashikawa
Wednesday PM, April 04, 2018
PCC North, 100 Level, Room 125 B
10:15 AM - EN03.04.01
How to Derive Intrinsic Potentials of HTS Materials by Controlling Cation Compositions
Jun-ichi Shimoyama1
Aoyama Gakuin Univ1
Show AbstractContinuous and eager efforts on the development of HTS materials have led their practical applications in various fields thus far. Very high Jc exceeding 1010 Am-2 at 77 K of coated conductors is now regarded as the lowest standard performance and highly reliable critical current properties of BSCCO tapes have been supporting the successful results of many research projects and development of new superconducting products. In addition, RE123 bulk materials are used for several applications, such as strong magnets, current leads, levitation systems and bearings. These suggests that critical current properties of these HTS materials are enough high against extensive practical applications. On the other hand, high production cost of HTS materials mainly due to a large number of fabrication processes to form highly grain aligned microstructure limits widespread of HTS applications. Our recent studies mainly on the effects of post-annealing at relatively high temperatures, 700~900°C, before oxygen annealing on superconducting properties of HTS indicated that precise control of nonstoichiometric cation composition is crucially important process to derive intrinsic potential of HTS. The cation composition is generally controlled by changing the starting composition, however, it unintentionally varies in the resulting materials depending on the sintering conditions, temperature, partial pressure of oxygen and external pressure. Even for Y123, which has been believed to have an exactly integral cation ratio Y:Ba:Cu=1:2:3, Y ion can substitute for Ba-site up to 2%. In the case of BSCCO, Sr-site is usually substituted by Ca and/or Bi, however, the substitution level can be controlled by applying the post-annealing process. Dramatically positive effects of precise control of cation composition near the integral ratio on superconducting properties, particularly on critical current properties, are shown for RE123, RE247 and BSCCO materials including challenges to reduce the electromagnetic anisotropy by doping and control of dopant level. Furthermore, new strategies to overcome weak-link problem at grain boundaries of HTS and the ultimate potential of HTS materials will be discussed.
10:45 AM - EN03.04.02
Electron Density Correlation with Superconducting Transition Temperature
Jose Alarco1,Peter Talbot1,Ian Mackinnon1
Queensland University of Technology1
Show AbstractWe describe an ab initio method to assist prediction of superconductivity in a solid using correlated real and reciprocal space determinants for known or unknown structures. Density functional theory (DFT) calculations for AlB2-type structures, show that the thermal energy (Te) associated with phonon anomalies displays one-to-one correspondence to the experimentally determined superconducting transition temperature (Tc)1. This correspondence is accurate for a range of conditions1-3 including different isotopes, metal substitution (e.g. Al, Ti or Sc) and changes in pressure (-5 GPa to 20 GPa) for MgB2. Similarly, we demonstrate correspondence of Te and Tc for other AlB2-type structures1 including BaSi2 and (Ca0.5Al0.5)Si2.
Using DFT, we evaluate electron density differences invoked by atom displacements aligned with phonon modes in MgB2 to show that the Fermi energy for the E2g mode alone accounts for the highly covalent B–B bond charge density distribution. Importantly, the band structure becomes tangential to the Fermi level and the Fermi surface undergoes a topological transition at a critical relative displacement of ~ 0.6% from the equilibrium real space position of boron atoms. The difference in Fermi energies at this critical displacement and at the equilibrium position corresponds to the superconducting energy gap. The volume between tubular σ surfaces in reciprocal space controls the depth of the phonon anomaly and is key to understanding superconductivity because it is directly related to the interplay between light and heavy mass σ bands at G near the Fermi level.
We extend this ab initio method to other superconducting structures including H3S and the hexaborides covering the range of experimental Tc values from <10 K to ~200 K for multi-element compounds. Hexaboride structures accommodate a wide range of metals with a corresponding range of electronic properties4. As with MgB2 and H3S, the calculated phonon dispersion (PD) for YB6 shows a similar proportionate inflexion in the T2g phonon mode for which the Te corresponds with measured Tc. These analyses are consistent with “extra” Raman and infra-red (IR) peaks observed in borides5,6 that imply lower symmetry superlattices are indicators of superconductivity even in cubic structures. Correlation of Fermi surface transitions with key modes in calculated PDs for variations in temperature, pressure or metal substitution shows that electron density distributions along bonds oriented with phonon mode directions are potential determinants of superconductivity.
1. Alarco, J. A., et al., Phys. Chem. Chem. Phys. (2015) 17 (38), 25090.
2. Mackinnon, I. D. R., et al., Comp. Mater. Sci. (2017) 130, 191.
3. Alarco, J. A., et al., Physica C: Supercond. and Applications (2017) 536, 11.
4. Mackinnon, I. D. R., et al., Mod. & Num. Sim. Mater. Sci. (2013) 3 (4), 158.
5. Alarco, J. A., et al., Phys. Chem. Chem. Phys. (2014) 16, 24443.
6. Bando, H., et al., J. Phys. Soc. Jpn. (2011) 80, SA053.
11:00 AM - EN03.04.03
Pinning-Induced Vortex System Disordering at the Origin of the Second Magnetization Peak in Superconducting Single Crystals
Lucica Miu1
National Institute of Materials Physics1
Show AbstractThe origin of the spectacular enhancement of the effective critical current density with increasing external magnetic field H, leading to a second magnetization peak (SMP) on the dc magnetic hysteresis curves of superconducting single crystals with random pinning, is still not clear. Many interesting SMP models and mechanisms have been proposed and considered so far, and it is believed at present that this effect is system dependent. However, by analyzing the dc magnetization relaxation in the SMP domain for various single crystal specimens (superconducting cuprates and iron-based superconductors), of different pinning strength, with H oriented along the crystallographic c axis or perpendicular to it, we found several sample independent, characteristic aspects, such as the absence of single-vortex collective pinning around the SMP onset field, and the sign changing of the vortex creep exponent between the onset field and the peak field. This general behavior and the peculiar disappearance of the SMP in certain underdoped cuprates and pnictides (attributed by us to the presence of SDW stripe-like static order) support strongly a continuous pinning-induced disordering of the low-H quasi-ordered vortex solid as the actual scenario for the SMP.
11:15 AM - EN03.04.04
Cuprate Physics Without Copper
José Lorenzana1,Jakub Gawraczynski2,Dominik Kurzydlowski2,3,Krzysztof Bienkowski2,Wojciech Gadomski2,Zoran Mazej4,Tomasz Jaron2,Andrzej Ozarowski5,Steve Hill5,Piotr Leszczynski2,Kamil Tokár6,Mariana Derzsi2,Paolo Barone7,Wojciech Grochala2
Istituto dei Sistemi Complessi-CNR1,University of Warsaw2,Cardinal Stefan Wyszynski University in Warsaw3,Department of Inorganic Chemistry and Technology4,Florida State University5,Institute of Physics, Slovak Academy of Sciences6,CNR-SPIN c/o Università dell’Aquila7
Show AbstractThe parent compound of high-Tc superconducting cuprates is a unique Mott state consisting of layers of spin-1 / 2 ions arranged on a square lattice, with a record high antiferromagnetic coupling within the layers, strong covalency between transition metal (TM) and ligands and no orbital degeneracy. There have been several attempts to replicate these characteristics with different TM ions. One proposal has been to use nickel(I) in place of copper(II). LaNiO2 is isoelectronic and isostructural with infinite layer parent cuprates, however, it lacks the strong covalent character between TM and ligand and the antiferromagnetic order has not been found. Sr2IrO4 has many similarities with cuprates including a robust antiferromagnetic order of spin-1/2 pseudospins. However, the correlated insulator character is much weaker and spin-orbit coupling effects dominate. I will discuss an alternative route where, to a large extent, these problems are solved and the physics of Cu(II) ions emerges without Cu.
11:45 AM - EN03.04.05
Revealing the Role of Nitrogen on Hydride Nucleation and Stability in Pure Niobium Using First Principles Calculations
Pulkit Garg1,Shreyas Balachandran2,Ilaksh Adlakha3,1,Peter Lee2,Thomas Bieler4,Kiran Solanki1
Arizona State University1,Florida State University2,Indian Institute of Technology Madras3,Michigan State University4
Show AbstractThe absorption of hydrogen and subsequent precipitation of hydrides degrades the superconductive properties of niobium. Although addition of dopant elements, particularly nitrogen, have shown improvement in the quality factor of superconducting radio frequency (SRF) niobium cavities, the underlying mechanisms associated with kinetics of hydrogen and the thermodynamic stability of hydride precipitates are not well known. Here, through first principles calculations, we report the effects of nitrogen doping on the energetic preference for hydrogen to occupy interstitial sites and the stability of niobium hydride. In particular, we show that the presence of nearby nitrogen significantly increased the energy barrier for hydrogen diffusion from one particular tetrahedral site to another interstitial site. Furthermore, the beta niobium hydride precipitate became energetically unstable up on addition of nitrogen in the niobium matrix. Through electronic density of states and valence charge transfer calculations, we find that nitrogen has a tendency to accumulate charge around itself, thereby decreasing the strength of covalent bonds between niobium and hydrogen atoms leading to an unstable state for both hydrogen and hydride. This explains the experimental observation i.e., niobium hydride is less stable in nitrogen doped niobium. Therefore, the presence of nitrogen during the processing of SRF cavities can play a critical role in controlling hydride precipitation and subsequent SRF properties.
EN03.05: Iron-Based and Boride Superconductors
Session Chairs
Carlo Ferdeghini
Eric Hellstrom
Wednesday PM, April 04, 2018
PCC North, 100 Level, Room 125 B
1:30 PM - EN03.05.01
Record Critical Current Density in Recent Fe-Based Superconducting Wires
Yanwei Ma1
Institute of Electrical Engineering, Chinese Academy of Sciences1
Show AbstractFor practical use it is essential to make Fe-based superconducting materials into wire and tape conductors with sufficient current carrying capability, which is limited by misaligned grains inside the conductors. The development of Fe-based superconducting wires at IEECAS has progressed rapidly resulting in improving the wire performance. A record transport critical current density (Jc) reaching 1.5 ×105 A/cm2 (Ic = 437 A) at 4.2 K and 10 T in Ba0.6K0.4Fe2As2 (Ba-122) tapes by texturing the grain orientation with optimized hot-press technique. The transport Jc measured at 4.2 K under high magnetic fields of 27 T is still on the level of 5.5 ×104 A/cm2. Moreover, at 20 K and 5 T the transport Jc is also as high as 5.4 ×104 A/cm2, showing a promising application potential in moderate temperature range which can be reached by liquid hydrogen or cryogenic cooling. The high-performance PIT Ba-122 tapes in this work suggest iron-based superconductors to be a strong potential conductor for high-field applications.
2:00 PM - EN03.05.02
Tuning Superconductivity in Epitaxial BaFe2As2 Thin Films by Tetrahedral Geometry Design
Jong-Hoon Kang1,Jong-Woo Kim2,Phillip Ryan2,Lu Guo1,Chirs Sundahl1,Jonathon Schad1,Y.G. Collantes3,Hellstrom Eric3,David Larbalestier3,Chang-Beom Eom1
University of Wisconsin1,Argonne National Laboratory2,University of Florida3
Show AbstractSignificant progress has been made in fabricating high-quality epitaxial thin films of iron-based superconductors. Strain engineering offers the possibility of tailoring the structural distortions at the atomic scale and enhancing superconducting properties. Here, we report that tetrahedral geometry driven by thin film strain leads to a significant enhancement of the superconducting transition temperature (Tc) of optimal Co-doped epitaxial BaFe2As2 thin films above the value of the bulk single crystals. We have found that the As-Fe-As bond angles were strongly modified by both epitaxial and thermal strains caused by the temperature-dependent lattice mismatch between BaFe2As2 thin films and the substrates. Synchrotron x-ray diffraction and resonant scattering demonstrate that the As-Fe-As bond angle and Tc are systematically tuned by in-plain strain and reach maximum Tc at the optimum bond angle of 109.5o. Strain engineering can provide a path toward tailoring superconducting properties and understanding superconductivity in other Fe-based superconducting thin films such as monolayer FeSe.
This work has been done in collaboration with J. H. Kang, P. J. Ryan, J. W. Lee, J. W. Kim, Y. Choi, J. Jiang, E. E. Hellstrom, D. C. Larbalestier.
** This was supported by the DOE Office of Basic Energy Sciences under award number DE-FG02-06ER46327.
3:30 PM - EN03.05.03
Interface-Induced Superconductivity at ~25 K at Ambient Pressure in Undoped CaFe2As2 Single Crystals
Paul C. W. Chu1,2,S. Y. Huyan1,L. Z. Deng1,K. Zhao1,Bing Lv3,Shuo Chen1,Zheng Wu1,Melissa Gooch1,Yimei Zhu4
University of Houston1,Lawrence Berkeley National Laboratory2,The University of Texas at Dallas3,Brookhaven National Laboratory4
Show AbstractSuperconductivity has been reversibly induced in undoped CaFe2As2 (Ca122) single crystals with Tc at ~25 K at ambient pressure and up to 30 K at 1.7 GPa. We found that Ca122 can be stabilized in two distinct tetragonal (T) phases: PI with a nonmagnetic collapsed tetragonal (cT) phase at low temperature and PII with an antiferromagnetic orthorhombic (O) phase at low temperature. Neither phase at ambient pressure is superconducting down to 2 K. However, systematic annealing for different time periods at 350 °C on the as-synthesized crystals reveals the emergence of superconductivity over a narrow time window. Detailed X-ray diffraction profile analyses further reveal mesoscopically stacked layers of the PI and the PII phases. The deduced interface density correlates well with the superconducting volume measured. The transport anomalies of the T-cT transition and the T-O transition are gradually suppressed over the superconductive region, presumably due to the interface interactions between the nonmagnetic metallic cT phase and the antiferromagnetic O phase. Our most recent STEM data display 8-20 nm domains in the superconducting Ca122 samples at 90 K. The results provide the most direct evidence to date for interface-enhanced superconductivity in undoped Ca122, consistent with the recent theoretical prediction. References: K. Zhao et al., PNAS 113, 12968 (2016); S. Y. Huyan et al., in preparation.
4:00 PM - EN03.05.04
Vortex Glass-Liquid Transition and Activated Flux Motion in NdFeAs(O,F) Thin Films
Jens Haenisch1,Kazumasa Iida2,Marco Langer1,Sandra Kauffmann-Weiss1,Taito Oomura2,Takuya Matsumoto2,Takafumi Hatano2,Hiroshi Ikuta2,Bernhard Holzapfel1
Karlsruhe Institute of Technology1,Nagoya University2
Show AbstractNdFeAs(O,F) thin films of around 50 nm thickness were grown by molecular beam epitaxy on MgO single crystal. The F doping was achieved by F-diffusion from a NdOF over-layer into the undoped NdFeAsO layer. The film showed a sharp cube-on-cube texture. Electrical transport properties were measured on laser-cut micro-bridges in 4-point geometry and maximum Lorentz force configuration in magnetic fields up to 14 T.
The T-dependent E(J) curves at constant magnetic field can by scaled within the framework of the vortex glass-liquid transition. Best scaling is achieved for 3D and critical exponent ν ~ 1.3 and z ~ 9. Whereas ν is in the expected range of 1.0-2.0, z is slightly above the expected range of 4.0-6.0. The reason for this increased value might lie in the distribution of pinning energies and, hence, local Jc variation. The activated flux motion within the vortex liquid range is characterized by analyzing the scaling behavior of the temperature-dependent resistivity curves as well as their derivatives.
The work was partly supported by the JSPS Grant-in-Aid for Scientific Research (B) Grant Number 16H04646.
4:15 PM - EN03.05.05
Intrinsic Interfacial Monolayers and Their Effect on the High-Temperature Superconductor FeSe / SrTiO3
Hunter Sims1,2,Donovan Leonard2,Axiel Birenbaum2,Zhouzhi Ge3,Lian Li3,Valentino Cooper2,Matthew Chisholm2,Sokrates Pantelides1,2
Vanderbilt University1,Oak Ridge National Laboratory2,West Virginia University3
Show AbstractIt was recently demonstrated that monolayer FeSe on a SrTiO3 substrate is a superconductor with Tc between 60 and 100 K, compared to 8 K in bulk FeSe. This is in contrast to the expected behavior; thinning a superconductor typically reduces Tc. Similar results have been obtained in monolayer FeSe deposited on BaTiO3 and anatase TiO2. In contrast, Tc has been measured to be only 3.7 K in bi-layer FeSe deposited on graphene (extrapolated to about 2 K in a monolayer), pointing to the major role of the interface in enhancing superconductivity. Here we determine the atomic structure of an interfacial layer and identify its role in driving the increase in Tc using a combination of quantum mechanical calculations and scanning transmission electron microscopy. Within our DFT calculations, this interfacial layer hosts long-range magnetic and orbital order not found in the typical TiO2 surface termination nor in previously identified surface reconstructions. Our calculations suggest the presence of a weak magnetic coupling between the interfacial monolayer and the deposited FeSe film, yielding a rich phase space of possible magnetic states. Interactions between this interfacial monolayer and FeSe generate symmetry-breaking distortions in the film that are favorable for increasing Tc and are not present in other possible FeSe / STO interface structures. We propose that this may provide a path forward toward the design and enhancement of other two-dimensional superconductors.
DFT calculations were supported by U.S. DOE grant DE-FG02-09ER46554 and the McMinn endowment at Vanderbilt University (HS, STP). They were performed at the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 (HS, STP). Work at ORNL is sponsored by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division (DNL, AYB, VRC, MFC). Work at West Virginia University (ZG, LL) is supported by the U.S. National Science Foundation, Division of Materials Research (DMR-1335215).
4:30 PM - EN03.05.06
High-Temperature Superconductivity in B-Doped Q-Carbon
Ritesh Sachan1,2,Anagh Bhaumik2,Siddarth Gupta2,Jagdish Narayan2
Army Research Office1,North Carolina State University2
Show AbstractWe report high-temperature superconductivity in B-doped amorphous quenched carbon (Q-carbon). This phase is formed after nanosecond laser melting of B-doped amorphous carbon films in a super undercooled state and followed by rapid quenching. Magnetic susceptibility measurements show the characteristics of type-II Bardeen-Cooper-Schrieffer superconductivity with a superconducting transition temperature (Tc) of 36.0±0.5 K for 17.0±1.0 atomic percent boron concentration. This value is significantly higher than the best experimentally reported Tc of 11 K for crystalline B-doped diamond. We argue that the quenching from metallic carbon liquid leads to a stronger electron-phonon coupling due to close packing of carbon atoms with higher density of states at the Fermi level. With these results, we propose that the non-equilibrium undercooling assisted synthesis method can be used to fabricate highly doped materials which provide greatly enhanced superconducting properties.
[1] Bhaumik, A; Sachan, R; Narayan, J. High-Temperature Superconductivity in Boron-Doped Q-Carbon. ACS Nano 2017, DOI: 10.1021/acsnano.7b01294.
4:45 PM - EN03.05.07
Non-Epitaxial Magnesium Diboride Films on Glassy Carbon Substrates
A. Baker1,Leonardus Bimo Bayu Aji1,John Bae1,E. Stavrou1,S. McCall1,Sergei Kucheyev1
Lawrence Livermore National Laboratory1
Show AbstractThin films of superconducting magnesium diboride are required for several applications. However, their fabrication can be challenging, particularly on amorphous or polycrystalline substrates when the film growth is inherently non-epitaxial. Here, we describe the fabrication and properties of 50-600-nm-thick MgB2 films on glassy carbon substrates, through optimizing parameters of Mg vapor annealing of sputter-deposited amorphous B films. Our results reveal a critical role of both the initial B film thickness and the temperature-time profile on the microstructure, elemental composition, and superconducting properties of the resultant films. We discuss the challenges related to the chemical reactivity of ultrathin B films, the control of nucleation and growth of MgB2 crystallites, and the formation of boron carbides at the film-substrate interface. We demonstrate the existence of a window of process parameters resulting in smooth superconducting films with thicknesses down to 50 nm. This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.
EN03.06: Poster Session: High Temperature Superconductors
Session Chairs
Wednesday PM, April 04, 2018
PCC North, 300 Level, Exhibit Hall C-E
5:00 PM - EN03.06.01
Fabrication of High Performance REBCO Coated Conductors with Artificial Pinning Centers by PLD Process
Yijie Li1,2,Linfei Liu1,Wei Wang1,Yanjie Yao1,Xiang Wu1,Tong Zheng1,Shunfan Liu1
Shanghai Jiao Tong University1,Shanghai Superconductor Technology Corporation2
Show AbstractREBCO superconducting tapes with different oxide nanoparticle additions have been fabricated on IBAD/MgO tapes by pulsed laser deposition process (PLD). For stoichiometric (123) REBCO films, it was found that when REBCO film thickness was smaller than 1.0 micrometer, REBCO superconducting films had a high critical current density Jc of 5.0x106 A/cm2 (at 77 K, self magnetic field) . As REBCO film thickness increased over 1.0 micrometer, the Jc values of REBCO films decreased with increasing of REBCO film thickness. X-ray diffraction (XRD) and high resolution scanning electron microscope (SEM) observation showed that a-axis orientation was easily formed in thick REBCO films. At higher substrate temperatures, BaCuO3 particles were also found in REBCO films. The main reason for lower Jc of REBCO thick films was broad grain boundaries. SEM and AFM observations showed that thick REBCO films had micrometer-scale grains and relatively broad grain boundaries which blocked superconducting current paths. In order to control the grain size and grain boundary width of REBCO thick films as well as to improve in-field superconducting properties, Y2O3, BaHfO3 and BaZrO3 addition effects were investigated. AFM, SEM and TEM images showed the presence of nano-scale Y2O3, BaHfO3, and BaZrO3 oxide particles in REBCO superconducting film. During deposition, these nanoparticles on REBCO film surface changed REBCO epitaxial growth process and acted as new crystal nucleus. By adding oxide nanoparticles into REBCO films, not only in-field superconducting properties but also surface morphology of REBCO films were obviously improved, which makes the growth of REBCO thick films to be easier. Four probe I-V curve measurements showed REBCO tapes with artificial pinning centers had excellent in-field performance. For 1.0 cm wide tapes, Ic was over 1000A (4.2K and 12T, H//c).
5:00 PM - EN03.06.02
Development of REBCO Thin Films with High Critical Current Properties on Metallic Substrates by Fluorine–Free MOD Method
Shuhei Ikeda1,2,Takanori Motoki1,2,Shin-ichi Nakamura1,Genki Honda3,Tatsuoki Nagaishi3,Toshiya Doi4,2,Jun-ichi Shimoyama1,2
Aoyama-Gakuin Univ.1,JST-ALCA2,Sumitomo Electric Industries, Ltd.3,Kyoto University4
Show AbstractREBa2Cu3Oy coated conductors have been widely manufactured by various methods. Among them, fluorine-free MOD (FF-MOD) method is one of the most cost-effective processes to prepare REBCO tapes because of simple chemical reaction under ambient pressure with very high processing rate. Our recent studies revealed that addition of moderate amount of hydrochloric acid to the starting solution resulted in generation of bi-axially aligned oxychloride Ba2Cu3O4Cl2 (Ba2342) fine crystals which assist biaxial growth of YBCO layers[1][2]. Therefore, highly textured YBCO films can be successfully prepared with high reproducibility in Cl-added FF-MOD method. In this study, further improvement of critical current(Ic) characteristics has been attempted for FF-MOD processed YBCO thin films on clad substrates covered by biaxially oriented oxide layers by increasing the thickness of YBCO layer.
Propionate-based solution with a nominal composition of Y: Ba: Cu: Cl = 1: 2.1: 3.15: 0.1 was coated on clad substrates by spin-coating. Coating and calcination at 500°C under the flowing oxygen atmosphere were repeated 1–9 times to control the film thickness. The calcined films were sintered in the tube furnace under flowing O2/Ar gas with PO2 = 10 Pa, followed by oxygen annealing at 450°C for 12 h. Ic values (A/cm) of the prepared films were evaluated by an inductive method in liquid nitrogen without an external field.
Optimizations of heat-treatment processes, such as calcination, sintering and oxygen annealing, for YBCO films (~0.5 mmt) resulted in a decrease in sum of all the heat-treatment time to half of the typical one with maintaining relatively high Ic ~90 A/cm. Ic of YBCO films with various thickness (0.17–1.5 mmt) sintered at 800°C for 1 h was highest (~100 A/cm) for a film with ~0.8 mmt and thicker films more than 1.0 mmt showed relatively low Ic due to an increase of impurity particles and/or generation of cracks. On the other hand, intermediate sintering was found to be effective for suppressing degradation of Ic for thick YBCO films. A YBCO film (~1.0 mmt) sintered twice exhibited higher Ic ~126 A/cm.
[1] T. Motoki et al., Supercond. Sci. Technol. 27 095017 (2014).
[2] T. Motoki et al., Supercond. Sci. Technol. 29 015006 (2016).
5:00 PM - EN03.06.03
Environmentally Benign Low-Fluorine YBa2Cu3O7 Nanocomposite Films with Preformed HfO2 Nanocrystals via Chemical Solution Deposition
Hannes Rijckaert1,Mika Malmivirta2,Nicolas Gauquelin3,Mark Rikel4,Sara Bals3,Michael Bäcker4,Katrien De Keukeleere1,Petriina Paturi2,Isabel Van Driessche1
Ghent University1,University of Turku2,University of Antwerp3,Deutsche Nanoschicht4
Show AbstractYBa2Cu3O7-δ (YBCO) coated conductors for electric power applications are demanding highly flexible and low-cost manufacturing processes. Up to now, textured superconducting YBCO films with the desired properties for the coated conductor architecture are mostly realized via vacuum processes such as pulsed laser deposition (PLD) and metal-organic chemical vapor deposition. These require costly high-vacuum systems, which are not attractive for industrial scale. Chemical solution deposition (CSD) is a non-vacuum technique and can fulfill demands such as cost-effectiveness, e.g. through high yield, and easy scalability. However, the pathway to fabricate YBCO nanocomposite films with relevant pinning properties does not seem to be easy because of the necessity to solve several critical issues related to YBCO growth. In the case of the self-assembled nanocomposite films produced via the PLD method, it has been already shown that the precise size tuning of secondary phases in YBCO matrix leads to improved pinning properties.
In this work, two different methods to synthesize HfO2 nanocrystals were introduced to reveal the influence of nanocrystal morphology and size on the defect state of YBCO matrix. This approach comes with some new specific challenges to tune the particle size for the CSD-based YBCO nanocomposite film starting from preformed nanocrystals. The solvothermal heating-up synthesis yielded highly crystalline nanorod-like HfO2 nanocrystals with a size of 2.6 nm in diameter and 8.0 nm in length. The microwave-assisted synthesis delivered highly crystalline HfO2 nanocrystals but now are spherical with a size of 6-8 nm in diameter.
For these two types of monoclinic HfO2 nanocrystals, we have shown the possibility to deposit the YBCO nanocomposite thin films starting from preformed HfO2 nanocrystals as nano-sized defects for flux pinning in combination with environmentally benign low-fluorine YBCO precursor solution on single crystal LaAlO3 substrates using a spin-coating technique. This CSD approach has been shown that the nanocrystal size and its distribution are the key parameters for a better control of structural defects in the YBCO matrix. Small particles of 5-20 nm would tend to promote formation of small planar defects (stacking faults) surrounding the particles, yielding an increase of microstrain and leading to high pinning force density of up to 17 GN m-3. Large particles (>25 nm) in the YBCO matrix could lead to formation of larger stacking faults leading to degradation of the critical current density in the YBCO nanocomposite films.
5:00 PM - EN03.06.04
Fabrication of RE–M–O Conductive Buffer Layer via Low-Temperature Liquid Phase Using Molten Alkaline Hydroxide
Shuhei Funaki1,Keisuke Soeda1,Yasuhiro Kojima1,Yasuji Yamada1
Shimane University1
Show AbstractIn the previous investigation, the development of REBa2Cu3Oy coated conductor (REBCO-CC) was promoted by using multi insulative buffer layer to restrain metallic element diffusion from the metallic tape substrate and to improve crystal orientation. Consequently, depositing of high-cost Ag layer to stabilize and protect from damage due to quenches are needed, and then it is difficult for production of REBCO-CC to lowering of overall cost. Recently, Doi et al suggested the novel REBCO-CC without Ag stabilizing layer structure, which substituted conductive buffer layer such as Nb:SrTiO3 and Nb:TiO2 for insulative buffer on Ni-electroplated Cube-textured Cu tape.
On the other, we suggested the production method of REBCO film via low-temperature molten alkaline hydroxide, is called “KOH flux method”. The KOH flux method can grow the biaxially crystal-aligned REBCO film on single crystalline substrate at below 500°C. Therefore, it is prospective technique for production of REBCO-CC to cost lowering. Moreover, recently we succeeded in the low-temperature fabrication of LRE–Ni–O (LRE = La, Nd) compounds by KOH flux method. The LRE–M–O compound has a conductive property in particularly case, accordingly, applying LRE–M–O layer to conductive buffer layer is expected. Conclusively, we can suggest that the novel technique for production of whole REBCO-CC by using low-temperature KOH flux method to fabricate conductive buffer layer and REBCO layer are established. In this report, we discussed correlation between depositional condition and obtaining phase, orientation for LRE–M–O films.
For preparing starting materials, LRE2O3 (LRE = La, Nd) and M–O powders were weighed with molar ratios of LRE : M = 1 : 1 and 2 : 1 respectively, and calcined at 1000°C for 24 h. Starting materials, KOH of 400 wt% to starting materials and LaAlO3 single crystalline substrate were put into alumina crucible, and heat-treated at 400–700°C for 12 h. All steps were performed at ambient pressure. After cooling to room temperature, the film and powder samples were extracted from the flux, and the obtained samples were washed by ultrasonic cleaning with distilled water and ethanol to eliminate the KOH and K2CO3. The grown phase, orientation, and lattice parameters were determined by X-ray diffraction (XRD) with a CuKa source. Surface morphology was obtained by optical microscope and scanning electron microscope (SEM).
In the case of La–Ni–O films, the LaNiO3 phase was synthesized at various depositional conditions, although phase stability and orientation deteriorated with increasing fabrication temperature. On the others, Nd–Ni–O films showed that the Nd2NiO4 phase was obtained mainly above 500°C in both Nd : Ni mixture ratios
5:00 PM - EN03.06.05
Crystallographic Phase Control and Island Formation in Fe1-xCuxSe Thin Films Grown by Pulsed Laser Deposition
Renato Camata1,Sumner Harris1
The University of Alabama at Birmingham1
Show AbstractThe intense research activity underway in iron-based superconductors, has included significant attention to FeSe due in part to its relative structural simplicity and promising characteristics for elucidating the physics of superconductivity in these materials. These characteristics include the highest critical temperature observed so far in iron-based superconductors (Tc ~ 65 K for an FeSe monolayer grown on SrTiO3), a nematic phase that is not suppressed when frustrated magnetic interactions suppress magnetic ordering, and Cooper pairing with orbital selectivity. FeSe-based alloys and chemical doping of FeSe can lead to additional attractive features such as control of Tc, altered nematic phase structure, possibly distinct pairing of charge carriers, and high Hc and Jc values, which are valuable in high magnetic field applications. In particular, doping of FeSe with Cu has been shown to be an effective way of switching superconductivity on and off in bulk samples of Fe1-xCuxSe. In this work, Fe1-xCuxSe thin films were grown on MgO (100) substrates via pulsed laser deposition. A KrF excimer laser (1.4–3.4 J/cm2) was used to ablate a pressed, sintered target produced by mixing powders of FeSe and Cu2Se precursor compounds at various concentrations. Targets were sintered in sealed quartz ampules at 700°C for 12 hours. Targets were ablated at pressures below 3.0x10-6 Torr with substrate temperature kept at 500°C. The thickness of all films was targeted at 400 nm as determined by deposition rate and scanning electron microscopy thickness calibrations. Films are analyzed by atomic force microscopy for surface morphology, and X-ray diffraction to characterize the crystalline structure of the films. We show that the surface morphology and crystallographic phase and orientation of the Fe1-xCuxSe films vary greatly with deposition conditions. Virtually all samples grown with x = 0 exhibit both, the tetragonal β-FeSe phase and the hexagonal δ-FeSe phase. It is also found that increasing the laser fluence in the 1.4–3.4 J/cm2 range, with the substrate temperature kept at 500°C, increased the fraction of β-FeSe in the films. Features of Stranski–Krastanov island growth are apparent in these samples for all deposition conditions explored with x = 0, suggesting that c-axis oriented β-FeSe islands grow on a δ-FeSe facet with a close epitaxial relationship to the tetragonal phase. This effect may allow the controllable growth of arrays of superconducting dots. Fe1-xCuxSe films with x = 0.010 and x = 0.015 are shown to be exclusively tetragonal, with the c-axis of the tetragonal structure oriented normal to the MgO substrate. These synthesis conditions correspond to the enrichment of selenium in the ablation target, since the Cu precursor used in the process (Cu2Se powder) is also a source of Se, which is consistent with the known sensitivity of the Fe:Se ratio on the stability of the crystal structure of this FeSe-based system.
5:00 PM - EN03.06.06
Effects of Over Pressure in 1st Sintering Process for Bi2223 Tapes
Ryo Koike1,Tomoyuki Tanaka1,Takanori Motoki1,Jun-ichi Shimoyama1,Yasuaki Takeda2,Takayoshi Nakashima3,Shin-ichi Kobayashi3,Takeshi Kato3
Aoyama-Gakuin Univ.1,The University of Tokyo2,Sumitomo Electric Industries, Ltd.3
Show AbstractAg-sheathed Bi2223 long tapes have been extensively used for various applications thus far particularly after the development of DI-BSCCO in 2004. DI-BSCCO is fabricated by two step sintering processes, 1st sintering under ambient pressure (PO2 ~ 8 kPa, ~840°C, ~100 h) to form the Bi2223 phase and 2nd sintering under high gas pressure (Ptotal = 30 MPa, PO2 ~ 8 kPa, ~840°C, ~100 h) after flat rolling for densification and controlling grain orientation. The overpressure sintering suppresses both generation of voids and degradation of c-axis grain orientation due to grain growth of Bi2223 [1]. Typical Ic of DI-BSCCO is 200 A at 77 K in self field [2]. On the other hand, sintering under low PO2 (< 5 kPa) was found to promote generation of Bi2223 from the precursor in our previous study[3]. Therefore, high Ic tape fabrication process could be designed by only 1st sintering under over pressure and moderately low PO2 (< 5 kPa). Based on these backgrounds, effect of over pressure in 1st sintering process on phase formation and superconducting properties of Bi2223 tapes have been investigated to develop high Ic Bi2223 tapes in a short fabrication time.
Through the systematic studies on 1st sintering as functions of temperature, time, Ptotal and PO2, the phase formation rate of Bi2223 phase was found to monotonically decrease with an increase of Ptotal. An increase in tapes thickness after sintering is smaller for tapes sintered under over pressure than that of tapes sintered under ambient pressure. These indicate that phase formation of Bi2223 somehow suppressed in a highly dense oxide filament, while the densification of filaments is preferable to achieve high Ic. In addition, c-axis lengths of tapes sintered under over pressure are apparently shorter than the standard tapes, suggesting promotion of substitutions of (Ca, Bi) and Pb for the Sr site and Bi site, respectively. Critical current properties of the tapes will be reported including the effect of post-annealing to control cation composition as well as carrier doping state.
[1] K. Sato, S. Kobayashi and T. Nakashima, Jpn. J. Appl. Phys. 51 (2012) 010006.
[2] T. Nakashima, S. Kobayashi, T. Kagiyama, M. Kikuchi, S. Yamade, K. Hayashi, K. Sato, G. Osabe and J. Fujikami, Cryogenics 52 (2012) 713–718.
[3] R.Tajima, J. Shimoyama, A. Yamamoto, H. Ogino, K. Kishio, T. Nakashima, S. Kobayashi and K. Hayashi, IEEE Trans. Appl. Supercond. 23 (2013).
5:00 PM - EN03.06.07
Topological Superconducting States of Niobium Films Induced by Electromagnetic Interaction with Nickel Nanowires Embedded in Porous Silicon Matrix
Vitaly Bondarenko1,Sergey Redko1,Eugene Chubenko1,Alexey Dolgiy1,Sergey Prischepa1,Hanna Bandarenka1,Carla Cirillo2,Carmine Attanasio2
Belarusian State University of Informatics and Radioelectronics1,Universita degli Studi di Salerno2
Show AbstractNowadays 1D semiconducting nanowire (NW) networks attracted significant interest because of their potential applications in the single-photon detectors, quantum-computing circuits and SQUID-like sensors. There are several approaches to fabricate 1D semiconducting NW network exist. In bottom-up approach ultra thin film of superconducting material deposited on top of the porous template with nanometer sized cells – porous alumina or porous silicon (PS), for example – and due to the very small thickness deposited material cover only surface of the template forming ordered network of superconducting NWs. However in another approach arrays of ferromagnetic NWs could be introduced in ordered porous templates providing regular magnetic arrays with characteristic dimensions, i.e. diameter of the NWs and nearest neighbor distance, in the nanometer range. Ordered array of ferromagnetic NWs serves as a source of periodic magnetic pinning centers in the superconducting film and matching effects between the artificial non-superconducting regular structure and the vortex lattice can be observed. The system behaves like a superconducting NW network when the coherence length is of the same order as the width of the channels between the non-superconducting areas. In this work we investigate the superconducting properties of a 30 nm thick Nb film sputtered on composite material consisting of an array of Ni NWs grown into a PS template. Nb film was electrically isolated from the ferromagnetic composite by an 8 nm insulating alumina layer.
Study of Tc(H) phase diagrams constructed by measuring resistive transitions of obtained samples in various perpendicular magnetic fields for several resistive transition criteria of the normal state resistance (10 – 90 % of normal resistance) revealed pronounced anomaly in the magnetic field values range 0.19-0.23 T where the critical temperature apparently increases with respect to what is conventionally expected, reaching a value that is almost equal to zero field critical temperature. Similar anomaly with lower amplitude is also present at higher fields, in the range 0.53-0.64 T. Samples were Ni NWs electrically interconnected with each other do not show such behavior. Measurements of magnetoresistance and voltammetric characteristics revealed that observed matching effects are more likely caused by the Little-Parks effect more than by the vortex pinning. Therefore, the system behaves like a 1D superconducting NW network where the confinement of the Cooper pairs is not caused by geometrical constrictions, but rather by the stray fields of the magnetic dipoles that modify the topology of the plain film creating regions where the superconductivity is strongly depressed.
This work is supported by Belarusian Republican Foundation for Fundamental Research, grant T16M-012.
5:00 PM - EN03.06.08
Quantum Electronic Stability of Freestanding ZrN Nanosheet with Dimensional Confined Superconductivity and Spin Density Wave
Yuqiao Guo1,Changzheng Wu1
Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China1
Show AbstractFree-standing 2D crystals mechanically cleaved from van der Waals solids exhibit unprecedented high crystal quality and macroscopic continuity which not only renovate the cognition that 2D long-range crystalline order cannot exist at finite temperature but also reveal the dramatic effect of dimensional crossovers on intrinsic physical properties. However, current progress is primarily limited to those typical strongly-anisotropic layered lattices and for the predominated 3D non-layered lattices whether their isolated atomic planes could survive in principle and if so how to two-dimensionalize those isotropic solids from their high symmetry parent crystals remains fundamental question and significant challenge. Herein, we theoretically proposed the quantum electronic stability of freestanding rock-salt ZrN nanosheet with critical-thickness of three atomic bilayers based on the electronic growth model. Along the way, we further experimentally realized ZrN vdW-like crystal via a bilayer-by-bilayer growth mode under CaH2-assisted topotactic reaction. The ZrN vdW-like crystals can be mechanically exfoliated and transferred in the same way as natural layered vdW materials and the step height in exfoliated layers is in good agreement with the height of critical-thickness calculated. The exfoliated high quality ZrN nanosheets with a few nanometres thick exhibits dimensional crossover effect of emerging spin density wave and 2D superconductivity with the unconventional upper critical field beyond the Pauli paramagnetic limit, which suggests a role for spin fluctuations in the pairing mechanism in dimensionally confined superconductors. The existence of critical thickness stability for 2D freestanding lattice and mild topotactic transformation process can be the general strategy to design and fabricate other high-quality 2D crystals in isotropic lattice, which further enrich the arena of artificial 2D materials and their confined new physics.
5:00 PM - EN03.06.11
Superconductivity and Surface Defects of In-Doped SnTe Nanostructures Grown by Chemical Vapor Deposition
Pengzi Liu1,2,Piranavan Kumaravadivel1,2,3,Yujun Xie1,2,Eric Miller4,Yuta Ebine4,Sungwoo Sohn1,2,Judy Cha1,2,5
Yale University1,Yale West Campus2,University of Manchester3,Hitachi High Technologies America, Inc.4,Canadian Institute for Advanced Research Azrieli Global Scholar5
Show AbstractBecause the topological protection of conducting surface states stems from the crystal symmetry for topological crystalline insulators (TCIs), crystal defects on the surface of TCI SnTe can strongly influence its topological and transport properties. As a derivative, In-doped SnTe was recently rediscovered as a candidate for time-reversal-invariant topological superconductors (TSCs) [1]. However, the high concentration of Sn vacancies inhibits surface states to be easily revealed [2], and the inhomogeneous distribution of In dopants in conjunction with catalyst impurities induced by chemical vapor deposition (CVD) may result in mixed behaviors of superconductivity [3]. Therefore, to manipulate topological and superconducting properties of In-doped SnTe, it is important to investigate how point defects, dislocations, surface topography and transport properties correlate with each other. We propose that the crystalline quality can be improved by suppressing the formation of surface defects on SnTe and In-doped SnTe micro/nanocrystals synthesized by CVD [4].
Our work focuses on the study of morphology-dependent superconductivity of In-doped SnTe nanostructures [3]. Superconducting transitions are obtained in transport measurements of In-doped SnTe nanostructures synthesized by CVD using gold nanoparticles as a catalyst. For nanoplates, complete superconducting transitions are observed at ~2.0 K, whereas lower-dimensional nanoribbons and nanowires present gradual and possible multiple transitions at lower temperatures of ~1.4-1.75 K. Saturating resistances in some nanowires also indicate incomplete superconducting transitions. We propose that inhomogeneity, such as surface In-doping inhomogeneity and gold impurities, is exaggerated in the transport measurements of smaller nanostructures, leading to variations of superconducting behaviors between different morphologies.
Moreover, to investigate surface defects that may degrade the topological characteristics of In-doped SnTe, we characterize surface pits, open cores and steps on {100} and {111} surfaces of SnTe micro/nanocrystals with and without In doping [4]. We show that enlarging, deepening, and faceting of the surface pits are enabled by sublimation of open cores and anisotropic movement of steps during natural cooling after the CVD growth. Distinct morphologies of surface pits arise from the crystal symmetry, surface termination, presence of In dopants, and dislocations of SnTe. Fast cooling suppresses the formation of surface pits, although growth conditions need to be optimized to decrease the density of dislocations that are responsible for the surface defects of SnTe micro/nanocrystals.
References:
[1] Sasaki,S., and Yoichi Ando. Crystal Growth & Design 15 (2015): 2748-2752.
[2] Novak, M., et al.. Physical Review B 88 (2013) 140502.
[3] Kumaravadivel P., et al.. APL Materials 5 (2017) 076110.
[4] Liu, P. et al.. Journal of Physics and Chemistry of Solids, DOI: 10.1016/j.jpcs.2017.12.016 (2017).
5:00 PM - EN03.06.12
Growth of Thin Mo2C Crystals on Cu Foil
Furkan Turker1,Goknur Cambaz Buke1
TOBB University of Economics and Technology1
Show AbstractIt is shown that many transition metal carbides (TMCs), such as Mo2C, WC, TaC and NbC, exhibit superconductivity which strongly depends on the crystal thickness. Here we show the CVD synthesis of thin Mo2C crystals on Cu foil by annealing Mo-Cu substrates in CVD system under methane flow. Grown crystals are characterized using Optical Microscope, Raman Spectroscopy, AFM, SEM with EDS and XRD. The effects of processing parameters on the thickness and morphology of the Mo2C crystals are discussed in order to explain the mechanism. This techniques may open the door to synthesis of other 2D TMC crystals.
Symposium Organizers
Paolo Mele, Muroran Institute of Technology and Shibaura Institute of Technology
Jens Haenisch, Karlsruhe Institute of Technology
Eric Hellstrom, Applied Superconductivity Center FAMU-FSU College of Engineering
Takanobu Kiss, Kyushu University
Symposium Support
Advanced Conductor Technologies
Research Institute of Superconductor Science and Systems, Kyushu University
Shanghai Creative Superconductor Technologies Co., Ltd.
Siemens AG, Corporate Technology
Supercoil Co., Ltd.
SuperOx Japan LLC, Sagamihara Incubation Center (SIC-3)
EN03.07: REBCO Coated Conductors—Advances in Flux Pinning
Session Chairs
Jongho Choi
Seung-Hyun Moon
Thursday AM, April 05, 2018
PCC North, 100 Level, Room 125 B
9:00 AM - EN03.07.01
High Performance REBa2Cu3Oy Coated Conductors with Artificial Pinning Center
Yutaka Yoshida1
Nagoya University1
Show AbstractWe have studied from the viewpoints of high speed deposition, large area, high performance of REBa2Cu3Oy coated conductors. High performance is determinedabout by optimum shapes of the artificial pinning centers (APC) in REBa2Cu3Oy (REBCO) coated conductors towards superconducting magnets operating at temperatures of 77 K or less.and lower temperature. Superconducting properties have been changedvary depending on the by different kind and addition amountquantity of BaMO3 added to REBCO. Therefore, we study the changes in theof shapes of nanorods shapedue to the difference in theof nature of additives and growth temperature. In addition, weand aim to control the APC having anwith the optimum shape that matchesing the operating temperature.
The high flux pinning performance was obtained for a 3.8vol.% BaHfO3 (BHO)-doped SmBa2Cu3Oy (SmBCO) on IBAD-MgO. At 77.3 K, the irreversibility field (Birr) of 16.8 T and the maximum flux pinning force density (Fp) of 32.5 GN/m3 (B//c) were achieved. In addition, the maximum Fp values of 400 GN/m3 and 120 GN/m3 for B//c were realized at 40 K and 65 K.
In particular, we describe the shape control of nanorods in SmBCO coated conductors by employingusing low temperature growth (LTG) technology using seed layers. From the cross- sectional TEM observations, weit was confirmed that using the LTG technique, the BHO nanorods, which were comparatively thin in diameter and short in length, formed athe fireworks structure in the case of SmBCO coated conductors. The superconducting properties in the magnetic field of the SmBCO- coated conductor on IBAD-MgO with the optimum amount of BHO showed that Fpmax = 1.5 TN / m 3 at 4.2K.
The high-speed growth technique for high performance REBCO coated conductor of the next task is an important subject. In this presentation, we will describe the development of the coated conductor fabricated with a combination a high repetition rate and a novel PLD growth. Thus far we have proposed a vapor-liquid-solid (VLS) method in which a thin liquid layer is interposed in the growing REBCO films with high quality and high speed. A VLS growth technique enables REBCO coated conductor to grow rapidly compared with the conventional PLD method. Furthermore, we will present the results such as introduction of APC for improving not only the fabrication speed but also the performance in the magnetic field of the VLS-RE123 coated conductor on the IBAD tape.
This work was partly supported by a Grant-in-Aid for Scientific Research (15H04252 and 16H04512). A part of this work includes the results supported by the ALCA project of the Japan Science and Technology Agency (JST) and NU-AIST alliance project.
9:30 AM - EN03.07.02
Systematic Studies to Enhance Flux Pinning of Y-Ba-Cu-O Superconducting Thin Films with M,N Nanophase Defect Additions
Timothy Haugan1,Mary Ann Sebastian2,1,Judy Wu3,Haiyan Wang4
Air Force Research Laboratory1,University of Dayton Research Institute2,U. of Kansas3,Purdue University4
Show AbstractThe addition of nanosize defects to YBa2Cu3O7-z (Y-Ba-Cu-O or YBCO) superconductor thin films have been studied by many groups world-wide, to enhance flux pinning and strongly increase critical current densities (Jcs). Since the first publications of this field in 2003 and 2004, over 6,200 citations have been listed for the subfield ‘flux pinning YBCO’, and the subfield ‘flux pinning’ has over 60,000 citations (source, Google Scholar). Despite many excellent systems studied, there are still new types of defect additions, flux pinning mechanisms, and processing methodologies to explore. This paper reviews and summaries studies in our lab from 2003 to 2018 on multiple YBCO+M+N systems, and presents recent interesting results on YBCO+Y2BaCuO5 films, achieving to our knowledge the largest defect sizes > 40 nm in YBCO-films so far. The pinning of this system is surprisingly different, by attaining > 10 vol% additions and strongly enhancing both strong anisotropic and weak isotropic pinning simultaneously. Thin films were made by pulsed laser deposition of (M/YBCO)X multilayer and (YBCO)1-x(M,N)x single-target films. Results and comparisons of flux pinning for different realms of T = 4-77 K, H = 0-9 T, and Theta = 0-90 degrees will be presented, and correlated with microstructure studies.
This work was supported by the AFRL Aerospace Systems Directorate and the Air Force Office Scientific Research (AFOSR).
10:30 AM - EN03.07.03
Enhanced Critical Current and Critical Temperature in Cuprate and Iron Based Superconductors by Practical Ion Irradiation Process
Qiang Li1
Brookhaven National Lab1
Show AbstractCuprate (RE)Ba2Cu3O7-d (RE = rare earth elements) high temperature superconducting (HTS) cables offer powerful opportunities for increasing capacity, reliability, and efficiency of the electricity grid. HTS coils can provide an alternative to rare-earth permanent magnets used in rotary machines and generators. Here, we present our recent studies carried out at Brookhaven National Laboratory’s Tandem Van de Graaff facility. We demonstrated a roll-to-roll irradiation process on production-scale cuprate HTS coated conductors that resulted in uniform enhancement of critical current up to 77 K at the dosage and ion energies readily accessible with commercial electrostatic generators. While great progress has been made in the applications of cuprate HTS, iron-based superconductors have attracted a great deal of interests in both fundamental physics and potential applications. We have grown iron-chalcogenide superconducting films on various single crystal substrates and metal substrates with enhanced transition temperature Tc, and carry high critical current density Jc.1,2 Recently, we developed a new route for simultaneous increase of Tc and Jc in iron-based HTS films by low-energy proton irradiation. Extensive transmission electron microscopy analysis provides direct atomic-scale imaging of cascade defects and the surrounding nanoscale strain field produced by low-energy proton irradiation.3 Tc is enhanced due to the nanoscale compressive strain induced by the irradiations and proximity effect, whereas Jc is doubled under zero field at 4.2 K through strong vortex pinning by the cascade defects and surrounding nanoscale strain. At 12 K and above 15 T, one order of magnitude of Jc enhancement is achieved in both parallel and perpendicular magnetic fields to the film surface. This robust, scalable and practical route opens up the possibility to improve both Tc and Jc in all superconductors [Ref. 1) Rep. Prog. Phys. 74, 124510 (2011). 2) Nat. Commun. 4, 1347 (2013). 3) Nat. Commun. 7, 13036 (2016).]
The author acknowledges the funding support from US DOE Office of Science, Materials Sciences and Engineering Division, and the US DOE, Advanced Research Project Agency-Energy, and collaborations with T. Ozaki, M. W. Rupich, L. Wu, W. Si, and V. Solovyov.
11:00 AM - EN03.07.04
Enhancement of the Critical Current Density by Ion Beam Induced Defects in High-Temperature Superconductors
Prashanta Niraula1,Eiman Bokari1,Shahid Iqbal1,Lisa Paulius1,Matthew Smylie2,Wai-Kwong Kwok2,Ulrich Welp2,Yifei Zhang3,Asghar Kayani1
Western Michigan University1,Argonne National Laboratory2,SuperPower Inc.3
Show AbstractThe critical current density (Jc) in High Temperature Superconductor (HTS) such as Y1Ba2Cu3O7-x (YBCO) can be enhanced by introducing defects into the material. These defects can act as pinning centers to restrict the motion of magnetic flux vortices, which as a result increases the current carrying capacity of a superconducting material. One method to create vortex pinning centers in the material is to introduce nanodefects during the synthesis process. Another is to use a post-synthesis ion beam irradiation technique to further induced defects onto an existing defect landscape within HTS to further enhance Jc. Particle irradiation provides a high precision method to optimize the defect landscape for critical current. We demonstrate that proton and oxygen beam irradiation can double the Jc of YBCO coated conductors with existing nano precipitates in fields of 6 Tesla parallel to the c-axis at T=27 K. In this work, HTS coated conductors containing Barium zirconate nanorods as pre-existing defects were irradiated with 50 MeV copper ions at angles of 0o, 15oand 30o from the crystallographic c-axis. We observed moderate enhancement of Jc at 5 K at high fields in samples irradiated at 30o and a suppression in others.
11:15 AM - EN03.07.05
Critical Currents in YGdBa2Cu3O7 and BaHfO3-Doped YGdBa2Cu3O7 up to 65 T
Boris Maiorov1,Maxime Leroux1,Fedor Balakirev1,Masashi Miura2
Los Alamos National Laboratory1,Seikei University2
Show AbstractWith the advent of all-superconducting very-high field (>20T) magnets, it becomes technologically relevant to study superconducting critical currents in magnetic fields in the range of 20 to 65 T. New challenges to vortex pinning understanding may also emerge at such very-high fields and low temperatures. For example, are thermal fluctuations as important at high-fields/low-temperatures as they are at liquid Nitrogen temperatures near the irreversibility line?
We present critical current measurements obtained by electrical transport measurements in pulsed magnetic fields up to 65T. The use of Fast Programmable Gate Array (FPGA) facilitates fast measurements/decision times permitting multiple current-voltage (I-V) curves measurements in a single magnetic field pulse lasting 50ms.
We study and compare standard YGdBa2Cu3O7 coated conductors with and without BaHfO3 nanoparticles grown by Metal Organic Deposition. These films have shown great results in terms of critical current enhancement up to 9T at high and low temperatures owing to the small size of BaHfO3 nanoparticles. Our results show continuous improvement for samples with BaHfO3 and will be analyzed in detail in the presentation.
11:30 AM - EN03.07.06
3D Printing of Designed YBa2Cu3O7-x Superconductor Bulks with Milled Powders for Applications
Xiangxia Wei1,Jun Ding1
National University of Singapore1
Show AbstractIt is well known that YBa2Cu3O7-x high temperature superconductor bulks can carry transport current in high magnetic field for many practical engineering applications. In this paper, three-dimensional YBCO compounts with designed shapes, high density and excellent superconducting properties were first successfully prepared by an extrusion-based additive manufacturing or 3D printing technique involving aqueous and non-aqueous pastes composed of milled precursors. The obtained milled powder can effectively reduce sintering temperature and simultaneously improve densification of YBCO compared with unmilled sample. Then, milled powder dispersed in aqueous and non-aqueous systems were printable to build YBCO part layer by layer, exhibiting shear thinning behaviors with the viscosity, density and porosity mainly related to their binder type and solid loading. It was found that non-aqueous PVB solution and high solid loading seemed to have a slightly positive effect on density, reaching up to 93% of theoretical density after just sintering at 940 oC for 10 h. To the end, a printed YBCO hollow cylinder with large trapped magnetic field demonstrated its ability of prolonging the levitation time, extending the potential application in flywheel technology. The integration of extrusion printing technique with milled precursors realizes the possibility of producing complex-shaped and scale-up YBCO with useful electromagnetic properties for a broad range of applications.
EN03.08: Superconducting Wires—Towards Applications
Session Chairs
Thursday PM, April 05, 2018
PCC North, 100 Level, Room 125 B
1:30 PM - EN03.08.01
Status of High Temperature Superconductors for High Field Magnets
David Larbalestier1
Florida State University1
Show AbstractLow temperature superconductors like Nb-Ti and Nb3Sn have enabled virtually all of today’s superconducting magnets including machines like the Large Hadron Collider with 8 T Nb-Ti dipole magnets and 1 GHz NMR spectrometers with 23 T field supplied by hybrid Nb-Ti/Nb3Sn magnets, presently the highest field all-superconducting user magnet. A recent NRC report [1] has described the scientific and technology rationales for many new types of ultra-high field superconducting magnet: regional 32 T superconducting magnets, a 40 T superconducting magnet, 28 – 37 T high-resolution NMR superconducting magnets, 25 – 40 T for x-rays and neutrons, 60 T DC, 20 T for human MRI, as well as magnets for fusion, particle-accelerators, radiotherapy, axion and other particle detectors. The materials and magnet technology have now made sufficient progress that a few of these magnets are now feasible. I will describe this progress and the various pluses and minuses of the three present high-temperature superconductor types and suggest some timelines under which high field coils beyond the capabilities of present-day Nb-Ti and Nb3Sn magnets might start to make it into commercial fabrication. At the NHMFL we have shown that High Temperature Cuprate Superconductors can generate test coils with fields of 45 T, almost twice the Nb-based superconductor limit and now equal to the world record 45 T DC field of the NHMFL User Magnet which requires 28 MW of DC power and a large 11 T Nb3Sn superconducting outsert magnet.
*Work carried out with many collaborators at the MagLab, especially with programs led by Huub Weijers, Denis Markiewicz (32 T), Ulf Trociewitz (Bi-2212 coils), Seungyong Hahn (NI REBCO), Scott Marshall (Bi-2223), Eric Hellstrom, Jianyi Jiang, and Fumitake Kametani (Bi-2212 conductors), and Dmytro Abraimov and Jan Jaroszynski REBCO conductors.
[1] B. I. Halperin BI et al., High magnetic field science and its application in the United States: Current status and future directions. Washington, D.C.: The National Academies Press, 2013. http://www.nap.edu/catalog/11211/opportunities-in-high-magnetic-field-science.
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2:00 PM - EN03.08.02
Exploring High Performance Superconducting Materials for the Future Circular Collider
Carlo Ferdeghini3,Marina Putti1,Amalia Ballarino2,Gianmarco Bovone3,Valeria Braccini3,Simon Hopkins2,Luca Leoncino3,Alessandro Leveratto3,Andrea Malagoli3,Pietro Manfrinetti1,Alessia Provino3,Antonio Siri1,Giulia Sylva1,Maurizio Vignolo3
Univ of Genova & CNR SPIN1,European Org Nucl Res2,CNR-SPIN3
Show AbstractThe proposed Future Circular Collider at CERN should reach a collision energy of 100 TeV thanks to a four times larger radius and double the magnetic field of the LHC. The latter requirement necessitates the development of superconducting materials/conductors with increased operating field.
Whilst most efforts are focused on Nb3Sn wires, this is an opportunity to assess the potential for high field application of newer superconductors. In the context of a collaboration between CNR-SPIN and CERN, we plan to investigate three different superconducting materials, i.e. Bi-2212, MgB2 and iron-based superconductors (IBS), with the scope of advancing their performance using industrially scalable production methods.
MgB2 conductors can be realised by the powder in tube (PIT) method and have the advantages of low cost and a relatively high critical temperature, Tc. However, the upper critical field, Hc2, and pinning in these conductors is still not optimised. Through the development of a boron precursor synthesis route, we plan to produce MgB2 nanopowders with the inclusion of controlled defects.
Bi-2212 wires realised by the PIT method have shown good performance at high fields. However, these results required heat treatment under pressure that is incompatible with the production of large coils for magnets. We plan to approach the performance today obtained by high pressure heat treatment through mechanical deformation and heat treatment sequences, including optimisation of the temperature profile and oxygenation conditions.
Recently discovered IBS exhibit high Tc and huge Hc2. PIT and coated conductor tapes have been successfully realised, with critical current values exceeding the threshold for practical application (105 A/cm2 at 10 T). We plan to develop prototype IBS conductors that achieve this critical current density at 16 T through reliable, simpler and scalable techniques that would permit industrialisation.
In this talk, the main goals and methods that we are developing will be reviewed.
3:30 PM - EN03.08.03
Development and Application of CORC® Cables and Wires Wound from HTS ReBCO Coated Conductors
Jeremy Weiss1,2,Danko van der Laan2,1,Dustin McRae1,U. Trociewitz3,Dmytro Abraimov3,Xinbo Hu3,David Larbalestier3,Chul Kim4,Sastry Pamidi4,Xiaorong Wang5,Hugh Higley5,Soren Prestemon5,Ramesh Gupta6,Tim Mulder7,8,Herman ten Kate7,8
University of Colorado Boulder1,Advanced Conductor Technologies2,National High Magnetic Field Laboratory3,Center for Advanced Power Systems, FSU4,Lawrence Berkeley National Laboratory5,Brookhaven National Laboratory6,CERN7,University of Twente8
Show AbstractIt’s been over 30 years since the discovery of high-temperature superconductivity, but the finicky intrinsic properties of these game-changing materials have required countless scientists and engineers to hone into a form that can now be applied as a true conductor technology on a macroscopic scale. Coated conductors, in which ReBCO thin films are deposited on a technical substrate utilizing a number of complex industrial processes, are finally becoming available from several vendors in long-lengths at costs that are likely to decrease in the coming years. The form-factor of coated conductors, an anisotropic tape with a high aspect-ratio, still presents a challenge in terms of cabling and winding into practical magnet systems. Studies on the strain-state within the ReBCO layer as a function of bending led to the development of the Conductor-on-Round-Core (CORC®) concept, in which several ReBCO coated conductors are wound helically around a relatively small former. These round, isotropic, HTS conductors offer a wide variety of operating currents and current densities to suit a range of applications. CORC® cables with thickness of 5 to 8 mm have been developed for power transmission and for use in large magnets, that require only very limited bending of the cable, or bundled into 6-around-1 cable in conduit conductors (CICC) for fusion and detector magnets. Much more flexible CORC® magnet wires with thickness of 2 to 4 mm are being developed for solenoids and accelerator magnets that require a current density (Je) of at least 300-600 A/mm2 at 20 T. An overview of the current status and future developments of CORC® cables and wires is presented here with an emphasis on conductor processing and application.
Acknowledgement
This work was in part supported by the US Department of Energy under agreement numbers DE-SC0007891, DE-SC0007660, DE-SC0009545, DE-SC0014009 and DE-SC0015775 and the U.S. Navy under contract numbers N00024-14-C-4065 and N00024-16-P-4071
4:00 PM - EN03.08.04
Recent Advances in Superconducting Bi-2212 Round Wire for High-Field Magnet Applications
Eric Hellstrom1,E. Bosque1,G. Bradford1,Michael Brown1,D. Davis1,C. English1,D. Hilton1,S. Hossain1,J. Jiang1,F. Kametani1,Y. Kim1,David Larbalestier1,J. Lu1,E. Miller1,G. Miller1,Y. Oz1,U. Trociewitz1
National High Magnetic Field Laboratory1
Show AbstractBi-2212 is the only cuprate superconductor that can be made as a round wire. It has high Jc and Hc2, can be fabricated with a variety of architectures, can be twisted and fully transposed as a Rutherford or a 6-on-1 cable, and can be lightly aspected to form a square or rectangular conductor. These characteristics are advantageous to design and build high-field magnets. Bi-2212 powder is now available from two sources, MetaMateria and nGimat, and short samples of wire made with nGimat powder have Jc = 9530 A/mm2 (4.2 K, 5 T) and Jc = 6860 A/mm2 (4.2 K, 15 T) with overpressure processing. Bruker-OST is fabricating > 1.4 km long Bi-2212 wire piece lengths with these powders. We have designed, modelled, wound, heat treated and tested coils that are Ic and stress/strain limited. There is good agreement between predictions from the models and the measured performance of the coils. This presentation will highlight the improvements in powders, wires, and heat treatments that underlie these advances in the performance of Bi-2212 wire.
4:15 PM - EN03.08.05
A Study of the Effect on Jc of Predensifying Superconducting Bi-2212 Round Wire at Different PO2, Temperature and Time
I. Hossain1,J. Jiang1,G. Bradford1,David Larbalestier1,Eric Hellstrom1
Florida State University1
Show AbstractAchieving high Jc in Bi2Sr2CaCu2Ox (Bi-2212) round wire requires overpressure heat treatment (OPHT) to eliminate current-limiting bubbles. The OPHT has a maximum temperature of 890 °C and is done with 50 bar overpressure with 1 bar oxygen partial pressure (PO2). During OPHT, the diameter of the Bi-2212 wire shrinks about 4%, with about 80% of this densification occurring during a 2 h hold at 820 °C before the Bi-2212 powder melts. As part of his PhD studies, Maxime Matras from our group investigated predensifying Bi-2212 round wire for 2 h at 820 °C at 50 bar overpressure with different PO2, followed by the full OPHT with 1 bar PO2. A surprising result of his study was that Jc of Ag-0.2 wt% Mg sheathed Bi-2212 round wire increased by more than 20% when the 820 °C predensification was done in 5 bar PO2, compared to predensification using 1 bar PO2. We are investigating what causes this significant increase in Jc and the processing parameters (t, T, PO2) to optimize this increase in Jc by predensification. This presentation will report on results of on-going predensification studies at temperatures ranging from 500 °C to 850 °C, at different PO2, for different times. Jc, irreversibility field, and critical temperature are being measured to determine the optimum heat treatment parameters. Scanning electron microscopy of fully-processed Bi-2212 wire is being used to understand the microstructure-property relationships.
4:30 PM - EN03.08.06
Evidence for Different Dopant Site Behavior by EXAFS in High Critical Current Nb3Sn Superconductor Wires
Chiara Tarantini1,Steve Heald2,Peter Lee1,Michael Brown1,Arup Ghosh3,David Larbalestier1
Florida State University1,Argonne National Lab2,Brookhaven National Laboratory3
Show AbstractTo meet Jc requirements for the Future Circular Collider (FCC) the high-field performance of Nb3Sn strands must improve. In the last decade the best in-field performance of Nb3Sn strands has been obtained by doping with Ti or Ta, however, these wires are far from homogeneous in phase or properties. It has been demonstrated that Ti doping can produce a more chemically homogeneous A15 layer in internal Sn wires and that it significantly narrows the distribution of properties (Tc, Hc2) [1]. However this occurs in a still significantly suppressed stoichiometry (23.1 and 23.4 at.%Sn in Ti and Ta doped wires, respectively). Moreover, the effects of doping is not fully understood: early studies suggested that both dopants preferentially substitute on the Nb site. But more recently, taking into consideration ternary compositions and the different effectiveness of Ti (1-2 at%) and Ta (3-4 at%) in changing the resistivity and obtaining the maximum Hc2, it was suggested that Ti might substitute on the Sn site. In order to resolve this conundrum and point to new ways to improve the Nb3Sn performance, we recently performed an Extended X-ray Absorption Fine Structure (EXAFS) study at the APS synchrotron in Argonne [2]. The EXAFS technique is sensitive to the local environment of a specific element in the structure and so it allows us to identify the site location of the dopants in modern high-performance Nb3Sn strands. We investigated Ti, Ta and Ta+Ti doped internal Sn wires and we found that, whereas Ti exclusively occupies the Nb site in the A15 structure, Ta unexpectedly occupies both sites. In particular we have determined that about 21-32% of Ta resides on the Sn site in the Ta-doped and the Ta+Ti doped wires. With such occupancies the (Nb+Ti):Sn ratio becomes strongly off-stoichiometry (~3.3-3.4) whereas the Ta and Ta+Ti doped samples become almost stoichiometric (~2.9-3.1), thus we have the paradox that the Ti-wires, which have the best performance of accelerator Nb3Sn wires, are the most off-stoichiometric.
Combining those findings with magnetic and specific heat characterization, we will discuss how the different occupancy affects the disorder and, as a consequence, the Hc2 behavior and the effect of charge doping in changing the A15 phase DOS. We will also discuss how this understanding could help to redesign an improved internal Sn strand for higher field application such as the 16T FCC project.
[1] C. Tarantini et al., Appl. Phys. Lett. 108, 042603
[2] S. M. Heald, C. Tarantini et al., in preparation.
Acknowledgements
APS supports: the US DOE-BES, the CLS and its funding partners, the Advanced Photon Source, the US DOE under Contract No. DE-AC02-06CH11357. NHMFL partial supports: the US DOE-SC, HEP under Award No. DE-SC0012083 and the NHMFL supported by NSF Coop. Agr. No. DMR-1157490 and the State of Florida.