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Volume 80, Issue 7
Displaying 1-16 of 16 articles from this issue
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Special Issue on High Performance Superconducting Materials —Progress of Microstructure Control—
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Hiroaki Kumakura, Kaname Matsumoto2016 Volume 80 Issue 7 Pages 395
Published: 2016
Released on J-STAGE: June 25, 2016
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Overview
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Goro Osabe2016 Volume 80 Issue 7 Pages 396-405
Published: 2016
Released on J-STAGE: June 25, 2016
Advance online publication: May 20, 2016JOURNAL FREE ACCESSBy using the CT-OP (Controlled Over-Pressure) sintering furnace, Sumitomo Electric (SEI) succeeded in improving various characteristics such as critical current and mechanical properties of Ag sheath Bi-2223 wire commercialized as DI-BSCCO. Recently, SEI has developed and commercialized high strength DI-BSCCO Type HT-NX wire reinforced with the Ni alloy tapes and has applied the residual axial compression after lamination. The critical tensile stress of Type HT-NX has reached 400 MPa at 77 K. For high field magnetic application such as NMR using Bi-2223 based superconducting wire reinforced with Ni alloy tapes is highly expected.
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—Relationship between Microstructure and Critical Current Characteristics—Yuh Shiohara, Koichi Nakaoka, Teruo Izumi, Takeharu Kato2016 Volume 80 Issue 7 Pages 406-419
Published: 2016
Released on J-STAGE: June 25, 2016
Advance online publication: May 27, 2016JOURNAL FREE ACCESSSince the discovery of the YBCO superconductor, many efforts have been made to develop useful superconductive wire and tape for many electrical power applications. Especially, the second generation coated conductors using REBaCuO (RE: rare earth element, Y, Gd, Sm, Nd, Eu etc) compounds have high expectations because of its high critical current density at the liquid nitrogen temperature and under self fields as well as high magnetic fields. Recently, several processes have been successfully developed to introduce effective magnetic flux pinning centers into the REBCO layer in order to enhance the in-field critical current densities. This paper reviews the present status of the research and development about the improvement of critical currents in considerations of nano-scale microstructure.
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Ataru Ichinise, Shun Miura, Kazuki Sugihara, Akihiro Tsuruta, Yusuke I ...2016 Volume 80 Issue 7 Pages 420-427
Published: 2016
Released on J-STAGE: June 25, 2016
Advance online publication: May 20, 2016JOURNAL FREE ACCESSBaMO3 (M=Hf, Sn)-doped Sm1+xBa2−xCu3Oy (x=0, 0.04) superconducting films were fabricated by pulsed-laser deposition (PLD). It is known that BaMO3 nanorods are formed in superconducting films and that the morphology of nanorods affects the superconducting properties, particularly the critical current density (JC) properties. In this study, superconducting films were fabricated by conventional PLD and by PLD using a low-temperature growth technique to control the morphology of the nanorods. The relationship between the nanorod morphology and JC properties is discussed.
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Toshiya Doi, Masayuki Hashimoto, Shigeru Horii, Ataru Ichinose2016 Volume 80 Issue 7 Pages 428-433
Published: 2016
Released on J-STAGE: June 25, 2016
Advance online publication: April 22, 2016JOURNAL FREE ACCESSLong length coated conductors (CCs) have recently become commercially available, serving as a promising candidate for use in electric power applications. However, the cost of materials and manufacturing is high, which discourages their use in widespread commercially feasible products.
REBa2Cu3O7 (REBCO; RE: Y or rare-earth elements) superconducting films with high critical current density (Jc) have been grown on cube-textured metal tapes for the purpose of developing CCs for high temperature, high magnetic field applications. In the standard approach, a biaxially crystal-aligned YBCO layer is deposited on a Y2O3/Y2O3-stabilized ZrO2/CeO2 buffered Ni-W tape. CCs become highly resistive when they are quenched, therefore, to manufacture reliable and safe applications, it is necessary to attach low-resistive metal layers such as Cu and/or Ag to the CCs to stabilize and protect from damage due to quenches. Presently, insulative oxides are used for the buffer layers, thus thick Ag and Cu layers are required to be deposited as the stabilizer layers on the YBCO layer. However, the high material and process costs for the Ag and Cu layers are one of the major obstacles for achieving low-cost CCs. Use of conductive buffer layers instead of the insulative ones will allow CCs to be less expensive. In this paper, we propose a new configuration for CCs: YBCO deposited on a conductive Sr(Ti0.95Nb0.05)O3 buffered Ni-electroplated {100}〈001〉 textured Cu and SUS316 lamination tape. Sr(Ti0.95Nb0.05)O3 was epitaxially grown on the Ni-electroplated {100}〈001〉 textured Cu tape and its resistivity was low as 2.5 mΩ-cm at 77 K. Excellent Jc of 2.6×106 A/cm2 was achieved at 77 K under a magnetic self-field for the YBCO/Sr(Ti0.95Nb0.05)O3/Ni/Cu/SUS316 tape. We believe that Sr(Ti0.95Nb0.05)O3 is one of promising candidates for the conductive buffer layer material.
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Yuma Kusafuka, Yusuke Ichino, Yutaka Yoshida, Ataru Ichinose2016 Volume 80 Issue 7 Pages 434-438
Published: 2016
Released on J-STAGE: June 25, 2016
JOURNAL FREE ACCESSIn order to improve critical current density (Jc) of REBa2Cu3Oy (RE: Rare Earth elements) films, it is effective to dope BMO3 (BMO, M=Zr, Sn, Hf, Sn, Nb) nanorods into the REBCO films. The shape of the BMO nanorods depends on the kind of materials. In this study, we doped Ba2SmNbO6 (BSNO) nanorods which has large lattice constant of 0.8518 nm into SmBa2Cu3Oy (SmBCO) films and observed their microstructure and superconducting properties. As a results, BSNO formed wide nanorods of which diameter and number density were about 40 nm and 200 /μm2, respectively. Jc-B curve of the BSNO-doped SmBCO film showed a Jc peak at 0.350 T at high measurement temperature. The peak field is almost the same with the matching field corresponding to the number density of BSNO nanorods. The irreversibility temperature also increased at almost the same magnetic field.
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Kazuki Sugihara, Yusuke Ichino, Yutaka Yoshida, Ataru Ichinose2016 Volume 80 Issue 7 Pages 439-442
Published: 2016
Released on J-STAGE: June 25, 2016
Advance online publication: March 18, 2016
JOURNAL FREE ACCESSWe report the longitudinal magnetic field effect on BaHfO3 (BHO)-doped-multilayered SmBa2Cu3Oy (SmBCO) films fabricated on single-crystalline substrates by pulsed laser deposition method. This longitudinal magnetic field effect was observed under the force-free state and this peculiar state caused the gain of the critical current density (Jc) with a peak against magnetic fields. We have reported that the Jc peak appears on multilayered SmBCO films with short BHO nanorods. In this study, we observed the remarkable Jc gain by up to 32% compared with the Jc in self-field. In addition, we measured the Jc-B curves at several temperatures.
Fig. 5 Fullsize ImageSchematic drawing of the pinned flux line near the film surface under the force-free state.View full abstractDownload PDF (1246K) -
Ryosuke Matsumura, Yutaka Yamada, Yasuo Hikichi, Ryusuke Hironaga, Tsu ...2016 Volume 80 Issue 7 Pages 443-446
Published: 2016
Released on J-STAGE: June 25, 2016
Advance online publication: March 18, 2016JOURNAL FREE ACCESSHigh Temperature Superconducting HTS current lead has been prepared by the TFA-MOD processed YBCO tapes. The YBCO tape has higher critical current density Jc and better magnetic property than the Bi2223 tape. Furthermore, thermal conductivity of YBCO tape with thin Ag layer is much lower than that of Ag-sheathed Bi2223 tape. The critical current of the YBCO tapes ranges from 150 A to 190 A in liquid nitrogen and self-field. A current lead is composed of eight YBCO tapes, Cu end caps and a pair of stainless steel boards. Rogowski coils and Hall sensors used for estimation of current distribution are attached on each YBCO tapes. The transport current of 1000 A was carried with no voltage on every YBCO tape at 77 K. The voltages between Cu cap and YBCO tapes almost linearly increased with increasing transport current, and they range from 0.206 mV to 0.234 mV and 0.210 mV to 0.230 mV at 1000 A, respectively. The low voltages correspond to 0.206 μΩ to 0.234 μΩ and 0.210 μΩ to 0.230 μΩ. The low contact resistance results in low joule heating at Cu joints. The current calculated by Rogowski coils in eight YBCO tapes varies from 4 A to 179 A at 1000 A and sweep rate of 200 A/s. Therefore, the imbalance among eight YBCO tapes is evaluated to be 175 A. The current of eight YBCO tapes calculated by Rogowski coils sums up to 1001 A, which is the slight difference of 1 A in comparison with transport current of 1000 A. Rogowski coils and Hall sensors are effective at evaluating of current distribution for current lead.
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Hiroshi Ohuchi, Yutaka Yamada, Naoya Kaneda, Hiroki Fujii, Hiroaki Kum ...2016 Volume 80 Issue 7 Pages 447-451
Published: 2016
Released on J-STAGE: June 25, 2016
Advance online publication: April 01, 2016JOURNAL FREE ACCESSMgB2 wires have been prepared by diffusion process using pure Mg metal tube. Amorphous B powder mixed with 5 mol% SiC nano-sized powder addition was encased in a Mg tube, and then the tube was inserted into a pure iron tube to form the Fe/Mg/B(powder) composite wires. The composite was drawn into a round wires of 1.0~0.8 mm in diameter without intermediate annealing. The composite wires were heat treated at 630℃ for 1~10 h in Ar gas atmosphere. Some of the specimens were hot pressed under 10 MPa and hot isostatic pressed (HIP) under 100 MPa during heat treatment. The MgB2 core was synthesized through the diffusion reaction between outer Mg metal tube and inner B powder. The MgB2 core forms denser structure without voids and cracks in comparison with conventional in-situ powder in tube (PIT) processed MgB2 wires. The Ic value at 4.2 K for the HIP treated MgB2 wire of 0.8 mm in diameter reaches to 31 A at 10 T, which corresponds to the Jc of 545 A/mm2. The Ic and Jc values are much higher than that of conventional PIT processed MgB2 wires.
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Hiroaki Kumakura, Shujun Ye, Akiyoshi Matsumoto, Ryuji Nitta2016 Volume 80 Issue 7 Pages 452-456
Published: 2016
Released on J-STAGE: June 25, 2016
JOURNAL FREE ACCESSWe fabricated in situ powder-in-tube(PIT) MgB2 wires using three kinds of Mg powders with particle size of ~45 μm, ~150 μm and 212~600 μm. Mg particles were elongated to filamentary structure in the wires during cold drawing process. Especially, long Mg filamentary structure was obtained for large Mg particle size of 212~600 μm. Critical current density, Jc, increased with increasing Mg particle size for 1 mm diameter wires. This is due to the development of filamentary structure of high density MgB2 superconducting layer along the wires. This MgB2 structure is similar to that of the internal Mg diffusion(IMD) processed MgB2 wires. However, Jc of the wires fabricated with 212~600 μm Mg particle size decreased and the scattering of Jc increased with decreasing wire diameter, while the Jc of the wires with ~45 μm Mg particle was almost independent of the wire diameter. The cross sectional area reduction of the Mg particles during the wire drawing is smaller than that of the wire. When using large size Mg particle, the number of Mg filaments in the wire cross section is small. These two facts statistically lead to the larger scattering of Mg areal fraction in the wire cross section with proceeding of wire drawing process, resulting in smaller volume fraction of MgB2 in the wire and lower Jc with larger scattering along the wire. SiC nano powder addition is effective in increasing Jc for all Mg particle sizes.
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Yutaka Yamada, Hiroshi Ohuchi, Akiyasu Yamamoto, Kohji Kishio2016 Volume 80 Issue 7 Pages 457-461
Published: 2016
Released on J-STAGE: June 25, 2016
JOURNAL FREE ACCESSWe have studied packing factor, microstructure, mechanical strength and trapped field of disk-shaped, polycrystalline bulk MgB2 samples with 20 mm in diameter prepared by hot-pressing with different applied pressures. The hot-pressed MgB2 bulk samples showed improved packing factor owing to shrinkage of the thickness by the uniaxial pressing. With an increase in packing factor, Vickers hardness increased from 470HV to 950HV and trapped field improved from 2.23 T to 3.39 T by the hot-pressing. Our results show that hot-pressing is one of the most effective techniques to extract superior trapped field performance of polycrystalline bulk MgB2 magnets through enhancing circulating supercurrent density and mechanical properties.
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Satoshi Demura, Yoshihiko Takano, Hideaki Sakata2016 Volume 80 Issue 7 Pages 462-467
Published: 2016
Released on J-STAGE: June 25, 2016
Advance online publication: June 10, 2016JOURNAL FREE ACCESSWe have succeeded in the electrochemical deposition of superconducting FeSe. Electrochemical deposition is a simple and low-cost method to obtain samples using an electrolyte and electrodes. The electrolyte is composed of 0.03 M FeCl2•4H2O, 0.015 M SeO2, and 0.1 M Na2SO4 dissolved in distilled water. We found that when the appropriate voltage is applied, FeSe was deposited on the substrate. Magnetic susceptibility measurements revealed a superconducting transition at approximately 8 K. These results open the novel fabrication method for superconducting tapes by the electrochemical synthesis.
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Aichi Yamashita, Yoshihiko Takano2016 Volume 80 Issue 7 Pages 468-472
Published: 2016
Released on J-STAGE: June 25, 2016
Advance online publication: June 03, 2016JOURNAL FREE ACCESSSuperconductivity of FeTe0.8S0.2 was successfully induced by a battery-like reaction found in a typical Li-ion battery. Excess Fe in FeTe0.8S0.2 was electrochemically de-intercalated and the superconducting properties were improved systematically by applying a voltage in both electrolysis citric acid aqueous solution and ionic liquid. This result suggests that this method can be used to develop new superconducting materials.
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Yoshimitsu Hishinuma, Hiroyasu Taniguchi, Akihiro Kikuchi2016 Volume 80 Issue 7 Pages 473-479
Published: 2016
Released on J-STAGE: June 25, 2016
Advance online publication: May 13, 2016JOURNAL FREE ACCESSIn the magnetic confinement type fusion reactor, we thought that the high critical current density (Jc) performance Nb3Sn wire will become the first candidate material for the future fusion magnet system due to its established industrial mass production and its technical achievements. However, the degradation of transport Jc property due to the high mechanical and thermal strains on the practical Nb3Sn wire is a serious problem to apply for the future fusion magnet to be operated under higher electromagnetic force environment. We developed the new bronze processed Nb3Sn wire using the Zinc (Zn) solid solution high Sn content bronze (Cu-Sn-Zn) alloy matrix for improvement of the mechanical strength by the solid solution strengthening. We also confirmed that the Zn promoted to diffuse between Nb and Sn elements, and that Zn homogeneously remained in the matrix after the diffusion reaction. In the Nb3Sn wires with various Cu-Sn-Zn-(Ti) alloy matrices, the non-Cu Jc value was increased by the two-stage heat treatment, and the maximum non-Cu Jc values under the external magnetic fields of 15 T and 18 T at 4.2 K were obtained about 420 and 160 A/mm2. The degree of Jc enhancement due to the two-stage heat treatment was estimated 30% higher compared with one-stage heat treatment. Change in the microstructure and the non-Cu Jc enhancement due to the two-stage heat treatment on the Nb3Sn multifilamenatry wire with various Cu-Sn-Zn alloy matrices were reported.
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Kyoji Tachikawa, Nobuya Banno, Yasuo Miyamoto2016 Volume 80 Issue 7 Pages 480-486
Published: 2016
Released on J-STAGE: June 25, 2016
Advance online publication: June 10, 2016
JOURNAL FREE ACCESSBronze processed and internal Sn processed Nb3Sn wires with a small amount of Ti additive are being widely used for ITER, NMR and other applications. However, heat treatment for Nb3Sn synthesis reduces the Sn concentration in the matrix to a few %. The wires then become mechanically delicate and must be handled carefully. As an alternative method to improve the mechanical properties of the wires, we choose gold brass (Cu-15 wt% Zn) as the matrix, which exhibits attractive mechanical performances. Two different processes have been applied to fabricate the wires, and then the diffusion behavior of each element in the wires has been investigated. EPMA results indicate good inter diffusion between brass matrix and Sn during heat treatment. Zn does not penetrate into Nb3Sn, and remains homogeneously in the matrix after the Nb3Sn synthesis, improving the mechanical tolerance of the wire. Moreover, Zn seems to be effective in accelerating the Nb3Sn synthesis. A Jc (without sheath) of 350 A/mm2 at 16 T and Bc2 of 25.5 T have been obtained at 4.2 K for the wire. The Jc of the wire may be improved by the optimization of filament configuration in future. React and wind process may be hopeful in the present new wires, which may extend the application area of Nb3Sn wires.
Fig. 9 Fullsize ImageLocal EPMA mappings of Sn on the cross section of inside of Nb sheath after the heat treatment at 700℃ for 200 h. (a) 0.6φ GB matrix composite-processed wire, and (b) 0.6φCu matrix composite-processed wire.View full abstractDownload PDF (5393K)
Review
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Kozo Osamura2016 Volume 80 Issue 7 Pages 487-496
Published: 2016
Released on J-STAGE: June 25, 2016
JOURNAL FREE ACCESSPractical superconducting (SC) wires are typical composite material consisting of SC layer/filaments together with functional components. In the present article, the commonality among composite microstructures for five kinds of the practical SC wires available in the market was emphasized. Their mechanical characteristics and the stress/strain dependence of critical current have been compared in conjunction of the local strain exerted on the SC component. Finally activity of the international standardization relating to the superconductivity was introduced.
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