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Author

Akira Ibi

Bio: Akira Ibi is an academic researcher from National Institute of Advanced Industrial Science and Technology. The author has contributed to research in topics: Pulsed laser deposition & Flux pinning. The author has an hindex of 20, co-authored 115 publications receiving 1432 citations. Previous affiliations of Akira Ibi include Niagara County Community College & The Furukawa Electric Co., Ltd..


Papers
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Journal ArticleDOI
TL;DR: In this paper, a columnar microstructure 10nm in diameter has been obtained by using Y123 targets including yttrium-stabilized zirconium for the pulsed-laser deposition.
Abstract: This paper describes the microstructure to improve the magnetic field dependence of the critical current density, Jc, of Y(RE)Ba2Cu3O7−x [Y(RE)123, RE: Gd and Sm] coated conductors. A columnar microstructure 10nm in diameter has been obtained by using Y123 targets including yttrium-stabilized zirconium for the pulsed-laser deposition. This columnar structure, composed of BaZrO3 and Y123, continued from the substrate to the surface of the film 0.25μm in thickness. We have named it “the bamboo structure” from its morphology. The bamboo structure was effective for increasing Jc in a magnetic field especially parallel to the c-axis. We have also found stacking faults in RE123 effective to improve Jc.

271 citations

Journal ArticleDOI
TL;DR: In this paper, a low volume fraction of a-axis orientated grains was obtained in the thick GdBa2Cu3O7?? (GdBCO) coated conductors (CCs) by the pulsed laser deposition (PLD) method on PLD-CeO2/ion-beam assisted deposition (IBAD)-Gd2Zr2O7 (GZO)/hastelloy metal substrate tapes.
Abstract: In order to increase the critical current, Ic, we have fabricated thick GdBa2Cu3O7?? (GdBCO) coated conductors (CCs) by the pulsed laser deposition (PLD) method on PLD-CeO2/ion-beam assisted deposition (IBAD)-Gd2Zr2O7 (GZO)/hastelloy metal substrate tapes. The highest critical current value was 522?A?cm?1 for a thickness of 3.6??m in self-field at 77?K. It was found that a low volume fraction of a-axis orientated grains was obtained in the thick GdBCO CCs, compared to YBa2Cu3O7?? (YBCO) CCs. Consequently, the GdBCO CCs showed higher critical current density (Jc) than YBCO CCs in all thicknesses from 0.2 to 3.6??m. Furthermore, we have succeeded in improving Ic in a magnetic field by the introduction of artificial pinning centres using a 5?mol% ZrO2 doped GdBCO target. In the measurement of the Ic dependence on the magnetic field angle, ?, Ic was much improved, especially at 0?, i.e., with the magnetic field parallel to the c-axis. The Ic value at 3?T was 59.5?A?cm?1 at 0? and it showed a minimum of 42.3?A?cm?1 at 82? for 2.28??m thick CC. The minimum value in the angular dependence of Ic at 3?T was about five times higher than that of YBCO CC and two times higher than that of pure GdBCO CC.

87 citations

Journal ArticleDOI
TL;DR: In this paper, the GdBa2Cu3O7?? (Gd-123) coated conductors by the pulsed laser deposition (PLD) method on PLD-CeO2/ion-beam assisted deposition (IBAD)-Gd2Zr2O7 (GZO)/hastelloy metal substrate tapes were presented.
Abstract: We prepared GdBa2Cu3O7?? (Gd-123) coated conductors by the pulsed laser deposition (PLD) method on PLD-CeO2/ion-beam assisted deposition (IBAD)-Gd2Zr2O7 (GZO)/hastelloy metal substrate tapes. The Gd-123 film showed a higher critical current density (Jc) in magnetic fields (B) and higher critical temperature (Tc) than those of YBa2Cu3O7?? (Y-123) film. The Gd-123 film exhibited a high Jc value of 0.19?MA?cm?2 at 3?T () in liquid nitrogen (77?K), and the Tc value was 93.8?K. The Jc value at 3?T was twice as high as that of Y-123 film. Moreover, the angular dependence in magnetic fields of Jc for Gd-123 was also superior to that of Y-123. The reduction of Jc by the magnetic field angle for Gd-123 was less sensitive than that in Y-123. Furthermore, Gd-123 clearly exhibited a peak at 0? () as well as at 90? () in the relationship of Jc on the magnetic field angle curve (Jc??), while Y-123 had no peak at 0?. These superior characteristics are considered to be due to the existing defects, such as stacking faults, as observed by transmission electron microscopy. PLD-Gd-123 coated conductors, with pinning-effective defects, high Jc and low anisotropy in Jc??, show promise for future applications.

63 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used a YAG laser to scribe the superconductive layer and applied post-annealing in an O2 atmosphere to oxidize the dross in order to increase the resistance.
Abstract: Expectations are high for using coated conductors for electric power applications not only because of better cost performance but also higher Jc–B properties compared with Bi2Sr2Ca2Cu3O10 (BSCCO) tapes. Furthermore, the coated conductors could also reduce AC losses by the use of various methods in post-treatment. When a YAG laser was used for scribing the superconductive layer, an AC loss reduction due to a decrease in the width of the superconductivity layer could be confirmed in short samples. In the case of AC applications using long tapes, high resistance between scribed filaments is necessary. However, the resistance between the filaments scribed by a laser was as low as 10−3 Ω cm−1. The reason for the low resistance was the existence of dross in the filament spacings, which was confirmed by a cross-sectional compositional mapping observation. Although the superconductivity layer was divided by the laser, the dross of the metal substrate made a bridge over the superconductivity filaments. Post-annealing in an O2 atmosphere to oxidize the dross was carried out in order to increase the resistance. Consequently, the resistance between the filaments was improved to be as high as 50 Ω cm−1. We succeeded in controlling the resistance value between filaments in a range five orders of magnitude higher than that of the as-scribed YBCO film, through oxygen atmosphere post-annealing.

55 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the Δ ϕ, R a value, amount of existing a-axis oriented crystals, and I c of YBCO coated conductor with increasing thickness.
Abstract: Thick YBCO film were deposited by the PLD method on the self-epitaxial CeO 2 buffered substrate: a CeO 2 cap layer was deposited by the PLD method on Gd 2 Zr 2 O 7 buffered Hastelloy tape by the IBAD method and highly texturing up to 4° was obtained. We have investigated the Δ ϕ , R a value, amount of existing a -axis oriented crystals, and I c of YBCO coated conductor with increasing YBCO thickness. To obtain YBCO coated conductors with high I c , good in-plane texturing of the CeO 2 layer is required. However, the value of I c saturated at a certain YBCO thickness, critical thickness, d c . As the YBCO thickness increased, the surface morphology became much rougher. Consequently, the surface temperature of YBCO becomes lower and the amount of a -axis oriented crystals in YBCO increased. Then, thick YBCO film exhibited d c . To solve this problem, we fabricated YBCO by multi-layer deposition using the Reel-to-Reel system, which was carried out at various temperatures. This process increases J c from 0.54 to 0.89 A/cm 2 .

54 citations


Cited by
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Journal ArticleDOI
TL;DR: The question is whether the advantages of superconducting wire, such as efficiency and compactness, can outweigh the disadvantage: cost.
Abstract: Twenty years ago in a series of amazing discoveries it was found that a large family of ceramic cuprate materials exhibited superconductivity at temperatures above, and in some cases well above, that of liquid nitrogen. Imaginations were energized by the thought of applications for zero-resistance conductors cooled with an inexpensive and readily available cryogen. Early optimism, however, was soon tempered by the hard realities of these new materials: brittle ceramics are not easily formed into long flexible conductors; high current levels require near-perfect crystallinity; and — the downside of high transition temperature — performance drops rapidly in a magnetic field. Despite these formidable obstacles, thousands of kilometres of high-temperature superconducting wire have now been manufactured for demonstrations of transmission cables, motors and other electrical power components. The question is whether the advantages of superconducting wire, such as efficiency and compactness, can outweigh the disadvantage: cost. The remaining task for materials scientists is to return to the fundamentals and squeeze as much performance as possible from these wonderful and difficult materials.

691 citations

Journal ArticleDOI
TL;DR: Angle-dependent critical-current measurements demonstrate that a strong and isotropic flux-pinning mechanism is extremely effective at high temperatures and high magnetic fields leading to high-temperature superconductors with record values of pinning force.
Abstract: Strong isotropic flux pinning in solution-derived YBa 2 Cu 3 O 7− x nanocomposite superconductor films

566 citations

Journal ArticleDOI
TL;DR: The controlled combination of two effective pinning centres (randomly distributed nanoparticles and self-assembled columnar defects) is shown to be possible and effective and to produce thick films with remarkable Ic(H) and nearly isotropic angle dependence.
Abstract: Retaining a dissipation-free state while carrying large electrical currents is a challenge that needs to be solved to enable commercial applications of high-temperature superconductivity. Here, we show that the controlled combination of two effective pinning centres (randomly distributed nanoparticles and self-assembled columnar defects) is possible and effective. By simply changing the temperature or growth rate during pulsed-laser deposition of BaZrO(3)-doped YBa(2)Cu(3)O(7) films, we can vary the ratio of these defects, tuning the field and angular critical-current (Ic) performance to maximize Ic. We show that the defects' microstructure is governed by the growth kinetics and that the best results are obtained with a mixture of splayed columnar defects and random nanoparticles. The very high Ic arises from a complex vortex pinning landscape where columnar defects provide large pinning energy, while splay and nanoparticles inhibit flux creep. This knowledge is used to produce thick films with remarkable Ic(H) and nearly isotropic angle dependence.

481 citations

Journal ArticleDOI
TL;DR: In this paper, a simple and practically scalable technique was used to produce long, nearly continuous vortex pins along the c-axis in YBa2Cu3O7?? (YBCO), in the form of self-assembled stacks of BaZrO3 (BZO) nanodots and nanorods.
Abstract: The development of biaxially textured, second-generation, high-temperature superconducting (HTS) wires is expected to enable most large-scale applications of HTS materials, in particular electric-power applications. For many potential applications, high critical currents in applied magnetic fields are required. It is well known that columnar defects generated by irradiating high-temperature superconducting materials with heavy ions significantly enhance the in-field critical current density. Hence, for over a decade scientists world-wide have sought means to produce such columnar defects in HTS materials without the expense and complexity of ionizing radiation. Using a simple and practically scalable technique, we have succeeded in producing long, nearly continuous vortex pins along the c-axis in YBa2Cu3O7?? (YBCO), in the form of self-assembled stacks of BaZrO3 (BZO) nanodots and nanorods. The nanodots and nanorods have a diameter of ~2?3?nm and an areal density ('matching field') of 8?10?T for 2?vol.% incorporation of BaZrO3. In addition, four misfit dislocations around each nanodot or nanorod are aligned and act as extended columnar defects. YBCO films with such defects exhibit significantly enhanced pinning with less sensitivity to magnetic fields H. In particular, at intermediate field values, the current density, Jc, varies as Jc~H??, with ?~0.3 rather than the usual values 0.5?0.65. Similar results were also obtained for CaZrO3 (CZO) and YSZ incorporation in the form of nanodots and nanorods within YBCO, indicating the broad applicability of the developed process. The process could also be used to incorporate self-assembled nanodots and nanorods within matrices of other materials for different applications, such as magnetic materials.

456 citations

Journal ArticleDOI
31 Mar 2006-Science
TL;DR: Benefits of the critical current in self-field as well as excellent retention of this current in high applied magnetic fields were achieved in the thick films via incorporation of a periodic array of extended columnar defects, composed of self-aligned nanodots of nonsuperconducting material extending through the entire thickness of the film.
Abstract: We demonstrated short segments of a superconducting wire that meets or exceeds performance requirements for many large-scale applications of high-temperature superconducting materials, especially those requiring a high supercurrent and/or a high engineering critical current density in applied magnetic fields. The performance requirements for these varied applications were met in 3-micrometer-thick YBa 2 Cu 3 O 7-δ films epitaxially grown via pulsed laser ablation on rolling assisted biaxially textured substrates. Enhancements of the critical current in self-field as well as excellent retention of this current in high applied magnetic fields were achieved in the thick films via incorporation of a periodic array of extended columnar defects, composed of self-aligned nanodots of nonsuperconducting material extending through the entire thickness of the film. These columnar defects are highly effective in pinning the superconducting vortices or flux lines, thereby resulting in the substantially enhanced performance of this wire.

413 citations