3M-M-O2 Sep 9 - Morning (10:30-12:30 PM)
Materials - LTS, BSCCO and others
10:30 - 11:00 Simultaneous measurement of critical current, stress, strain and lattice distortions in different high temperature superconductors|
SCHEUERLEIN Christian1, BJOERSTAD Roger1, RIKEL Mark2, HUDSPETH Jessica3, SUGANO Michinaka4, BALLARINO Amalia1, BOTTURA Luca1
1CERN, Switzerland, 2Nexans, Germany, 3ESRF, France, 4KEK, Japan
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The electromechanical properties of different cuprate high temperature superconductors, notably two ReBCO tapes, two multifilament Bi-2223 tapes and a multifilament Bi-2212 round wire are compared at 77 K in self field. For the first time the critical current, stress, strain and lattice parameter changes of the different conductor phases have been measured simultaneously in a high energy synchrotron beamline. The experiment with 15 cm-long straight samples that are free to contract during cool down enables to gauge the intrinsic conductor strain limits and to compare them directly to the lattice distortions.
11:00 - 11:15 Continuous Fabrication of large area Bi-2212 Superconducting Coatings|
LALIENA Carlos1, LENNIKOV Vassili1, REY-GARCÍA Francisco1, AMAVEDA Hippolyte2, MORA Mario1, MOYA Sara3, RUIZ Óscar3, DE LA FUENTE Germán1, ANGUREL Luis1
1ICMA (CSIC-University of Zaragoza), Spain, 2ICMA (CSIC-University od Zaragoza), Spain, 3Torrecid S.A., Spain
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Laser technologies have been widely used to process high temperature bulk materials and coatings in planar geometries. Bi-2212 materials show an incongruent melting and the anisotropy that appears during solidification induces a high degree of texture in the annealed samples. We have recently patented a device that combines the use of a laser and a continuous furnace. This system can be used to process planar samples with the laser scanning the sample surface while the material is moving inside the furnace.
The objective of this work is to present a procedure to thermally process superconducting coatings with sizes that can reach values higher than 50 cm2. This method entails the use of commercial continuous furnaces that can be easily scaled to any size and allow for uniform sample movement.
In order to reduce the price of the superconducting powders, we have analysed the possibility of using different degrees of reaction in the precursors. Starting from the initial metal compound component mixture, we have performed different heat treatments in a continuous furnace and have determined which is the minimum degree of reaction in these powders that can reach a superconducting sample at the end of the process.
Pressed and substrate-coated precursors were textured using this process. Alumina plates with SrZrO3 buffer layers were used as substrates. The samples were textured using a laser induced melting zone process within the laser furnace. Samples of 5 or 10 cm width were processed, although the system allows to process samples up to 60 cm width. The influence of several laser parameters in the microstructure of the laser-processed samples was analysed using electron microscopy.
Transport properties were measured after annealing, in particular the temperature dependence of the resistivity and the transport critical current values at 77K. Critical temperature values of the order of 85 K have been obtained and critical current values higher than 200 A/cm-width were measured.
This work was supported by the Spanish Ministerio de Economía y Competitividad and the European FEDER Program (project MAT2011-22719), by the Gobierno de Aragón (research groups T12 and T87) and by CERAMGLASS project (EU LIFE programme LIFE11 ENV/ES/560). We acknowledge the use of SAI, Univ of Zaragoza.
11:15 - 11:30 Optimization of Bi-2212 High Temperature Superconductors by Potassium Substitution|
SHENGNAN Zhang1, CHENGSHAN Li1, QINGBIN Hao1, XIAOBO Ma1, PINGXIANG Zhang1
1Northwest Institute for Nonferrous Metal Research, China
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Since the first discovery of Bi2Sr2CaCu2O8+d (Bi-2212), it has been considered to be one of the most promising high-temperature superconductors (HTS) due to its excellent properties under low-temperature, high magnetic field conditions, including the high irreversibility field beyond 100 T and high critical current density under high magnetic field. Polycrystalline bulks of Bi2Sr2Ca1-xKxCu2O8+d (Bi-2212) with K doping content of x=0, 0.05, 0.10 and 0.15 were fabricated by spark plasma sintering technique. The influences of K doping on the microstructures, electronic structures, as well as the related superconducting properties were systematically investigated. The XRD analyses confirmed that K+ ions have successfully substituted into the matrix of Bi-2212, and lead to a systematical change of lattice parameters. Due to the change of thermodynamic properties, bulks with higher density, larger grain size and better texture structures were obtained after doping. Therefore, AC susceptibility measurement revealed the optimization of intergrain connections, which lead to the optimization of both self- and in-field critical current density, Jc of this system. The optimization of microstructures also caused the enhancement of surface pinning. Based on the enhancements of both intergrain connections and flux pinning properties, an obvious improvement of critical current density was obtained with the optimal doping content of K=0.05. Meanwhile, Bi-2212 single filament tapes with K doping content of 0 and 0.05 were also fabricated by powder in tube process. The XRD patterns also proved the successful doping of K ions in Bi-2212 matrix. And the critical current density Jc, measured by transport method under the magnetic field from 0 to 20 T at 4.2 K, proved the effectiveness of K doping on the enhancement of flux pinning properties of Bi-2212. This work provides a new possibility for the further enhancement of critical current density in Bi-2212 wires for practical applications.
Sincerely acknowledge the equipment supports from EMFL during the magnetic field measurement with 20 T magnet in Grenoble. This research was financially supported by National “973” Project, No. 2011CBA00104, and National Natural Science Foundation of China No. 51472206.
11:30 - 11:45 Key microstructures in high Jc Bi2212 round wires: Are there any lessons for making round wires of other HTS materials?|
KAMETANI Fumitake1, JIANG J.1, MATRAS Maxime1, ABRAIMOV D.1, SCHEUERLEIN Christian2, TROCIEWITZ Ulf1, HELLSTROM Eric1, LARBALESTIER David1
1National High Magnetic Field Laboratory, United States, 2European Organization for Nuclear Research (CERN), Switzerland
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Bi2Sr2CaCu2Ox (Bi2212) is so far the only HTS cuprate with which high Jc can be developed in multiple architectures, round, multifilament and in the twisted state that benefits low hysteretic losses, isotropic properties and high magnetic field quality. Especially now that the Bi2212 filament density can become almost 100% by overpressure processing, Jc reaches 2500 A mm-2 at 20 T, 4.2 K. But why high Jc is possible in Bi2212 round wires rather than only in the anisotropic tape form (in order to reduce or eliminate deleterious high angle grain boundaries (HAGBs)) demanded by all other HTS is a hugely important question. We have been extensively studying the grain and grain boundary (GB) structure in Bi2212 round wires in comparison with that found in Bi2223 (Bi2Sr2Ca2Cu3Ox) flat tapes by employing high resolution electron backscatter diffraction orientation imaging microscopy (EBSD-OIM). The key finding is that there is a very marked texture in melt-processed Bi2212 round wire and that the texture is, very surprisingly, biaxial. Consistent with these observations, Bi2223 flat tape shows Jc-H hysteresis with increasing and decreasing field that is characteristic of weak-linked systems, whereas there is no hysteresis in the Bi2212 round wire and no weak link problem in the Bi2212 wire. In addition Jc(H) at 4.2 K of round wire Bi2212 is about 3 times higher than that of flat tape Bi2223. Growth-induced texture that develops as Bi2212 nucleates and grows during the heat treatment appears to be the key step in generating this highly-desirable microstructure. This presentation will also discuss how the grain texture depends on the local architecture such as the filament diameter, filament-coupling, bonding and other parameters. We will also address the broader issue of what characteristic are needed to allow similar properties in other HTS cuprates.
11:45 - 12:00 Superconductivity above 77 K in Pb1212 Epitaxial Films|
SACHIO Komori1, ITSUHIRO Kakeya1
1Kyoto University, Japan
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Recently, we have found that Pb1-ySr2Y1-xCaxCu2+yO7+δ (Pb1212), whose crystal structure is similar to YBCO, has small anisotropy (γ ≈ 10) and highly underdamped intrinsic Josephson junctions. Various superconducting transition temperature (Tc = 10～90 K[3,4]) have been reported for Pb1212: Higher Ca concentration x gives rise to higher Tc. However, the presence of the large amount of impurity phase in large x samples makes difficult to obtain a single crystal. We report the first observation of superconductivity above 77 K in single phase Pb1212 epitaxial films. Pb1212 epitaxial film has been grown by a two-step technique consisting of a low-temperature sputtering step and a high-temperature ex-situ growth step. Subsequent air annealing and quenching treatment have also been performed to make the film superconducting. The results of out-of-plane x-ray diffraction measurements indicate the absence of impurity phase and complete c-axis alignment of the film. The results of in-plane x-ray diffraction measurements indicate that the film grow epitaxially on the SrTiO3 (100) substrate. The maximum Tc,onset attained in the present study is 88 K.
12:00 - 12:15 multilayered NbN/AlN structure to increase critical field for superconducting Radiofrequency Cavity.|
MARCHAND Benoit1, MARTINET Guillaume1, FORTUNA Franck2, BAUMIER Cédric2, ANTOINE Claire3
1IPN, Orsay, France, France, 2CSNSM, France, 3CEA/DSM/IRFU, France
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Actual particles accelerators are using Superconducting Radiofrequencies (SRF) cavities made of either bulk Niobium or bulk-like Niobium films. Nevertheless, this technology has an intrinsic accelerating gradient limit of ~60 MV/m with optimal cavities design (ILC shape) at 1.8K. This limit is induced by the maximum surface magnetic field (Hsh ~200 mT) that bulk Niobium can hold before quenching. Theoretical model  predict that decreasing the film thickness below the characteristic penetration length of type II superconducting alloys films could lead to an increase of Hc1 and prevent vortex nucleation. By separating superconductor films with insulator thicker than coherence length, multilayer structures (Superconductor/insulator/superconductor –SIS) could be formed on the top of cavity wall and could screen the effective magnetic field seen by bulk Niobium. With a short coherence length of ~5 nm and a relatively large penetration length of ~200 nm NbN is an excellent candidate for such structure.
In this contribution, we will present the experimental study of the screening effect based on NbN/AlN multilayers. The first challenge was to produce high purity NbN/AlN multilayer structure. Therefore, we used molecular beam epitaxy and played with different thicknesses in order to maximize the critical field. Preliminary results on the structural and superconducting properties of those multilayers will be presented. In parallel, superconductivity behavior of a 4 layers SIS under RF regime was characterized with a pill-box cavity working in the TE011 mode.
 A. A. Abrikosov, JETP, 19, 988 (1964)
 A. Gurevich, Applied physics letters 88, 012511 (2006)
 C. Z. Antoine, J.-C. Villegier and G. Martinet, Applied Physics Letters, 102(10), 102603 (2013)
This work was supported by P2IO
12:15 - 12:30 Microstructure of Pb-free superconducting solders |
AKSOY Canan1, MOUSAVI Tayebeh1, GROVENOR Chris1, SPELLER Susannah1
1Oxford University, United Kingdom
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Microstructure of Pb-free superconducting solders
C. Aksoy 1,2, T. Mousavi1 , C.R.M. Grovenor1 and S.C. Speller1
1Department of Materials, University of Oxford, UK
2Department of Electric & Electronic Engineering, Euroasia University, TUBITAK, Turkey
New restrictions on the use of Pb alloys will soon become a serious concern for superconducting magnet manufacturers who often use Pb-Bi alloys as superconducting solders. We are studying the binary Sn-In and ternary Sn-In-Bi systems as potential replacements for these Pb-Bi alloys for superconducting joints between NbTi superconducting wires. A range of binary and ternary compositions have been fabricated into 2-mm cylindrical bulk samples, and the influence of both chemistry and microstructure on the superconducting properties have been investigated using analytical scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and SQUID magnetometry.
Phase mapping in the analytical-SEM has shown that in the Sn-In binary system the volume fractions of β and γ-phase can be easily controlled by choice of composition and quenching rate. The TC and upper critical field (HC2) values can be enhanced by increasing the volume fraction of In-rich β-phase, and the Sn content in solid solution in the β-phase also controls the superconducting properties of the β-phase. The ternary Sn-In-Bi alloys can contain γ and β-phases as well as both BiIn and BiIn2 depending on the initial alloy composition chosen, and have complex fine scale microstructures. The best superconducting properties so far have been measured in a Sn35In50Bi15 composition consisting of a majority phase β-phase with a fine eutectic of γ and BiIn2.