S. Miyata

Investigation of thick PLD-GdBCO and ZrO2 doped GdBCO coated conductors with high critical current on PLD-CeO2 capped IBAD-GZO substrate tapes

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.

Magnetic field dependence of Jc for Gd-123 coated conductor on PLD-CeO2 capped IBAD-GZO substrate tapes

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.

Development of long GdBCO coated conductor using the IBAD/MPMT-PLD method

We have developed long GdBa2Cu3O7−X (GdBCO) coated conductors by a multi-plume and multi-turn pulsed laser deposition (MPMT-PLD) method and have successfully fabricated 32 and 60.7 m long GdBCO coated conductors with a high critical current, Ic, and high deposition rate. The Ic of the 32 and 60.7 m long GdBCO coated conductors were 205 A (Jc = 1.36 MA cm−2) and 183 A (Jc = 1.45 MA cm−2), respectively, at 77 K and 0 T. In addition, they exhibited higher Ic values in a magnetic field than a YBa2Cu3O7−X (YBCO) coated conductor: typically 20 A at 77 K and 3 T while the value for a YBCO coated conductor is 8 A. These high Ic values are due to the smaller number of a-axis oriented grains in GdBCO than in YBCO. Furthermore, the speed of production of the GdBCO layer was increased to 10 m h−1 while that of the former YBCO coated conductor was 3.75 m h−1. The material yield of long GdBCO layers using the MPMT-PLD method was about 26–28%. The high Ic of GdBCO in a magnetic field, the high production rate and the high material yield are promising for applications.

Progress of PLD and IBAD processes for YBCO wire in the SRL-Nagoya Coated Conductor Centre?new method for a coated conductor using a self-epitaxial PLD-CeO2 buffer

The Nagoya Coated Conductor Centre (NCCC) in SRL has installed new reel-to-reel IBAD and PLD systems for the fabrication of long, coated conductors. A 53?m long ion-beam assisted deposition (IBAD) substrate has been successfully produced. The degree of bi-axial texturing was improved by the newly found buffer deposition technique of pulsed laser deposition-?(PLD)-CeO2, which we call the self-epitaxial method. The PLD-CeO2 layer brought about a high degree of in-plane texturing up to 2.6? in a few minutes on an IBAD seed layer. The resultant YBCO coated conductor on the CeO2 layer showed high Jc values of up?to 4.4?MA?cm?2. The reel-to-reel PLD equipment with a high power laser of 200?W is now being applied to long-conductor fabrication and CeO2 buffer layer deposition with a high deposition rate.

Development of a laser scribing process of coated conductors for the reduction of AC losses

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.

Current status of pulsed laser deposition YBCO coated conductors in SRL using buffer layers by ion-beam assisted deposition GZO and self-epitaxy pulsed laser deposition CeO2

For a long coated conductor fabrication, SRL-Nagoya Coated Conductor Center (NCCC) has installed reel-to-reel equipment for IBAD and PLD systems. A 60 m long IBAD and a 55 m CeO2 capped substrate have been successfully produced. The PLD-CeO2, which we call the self-epitaxial method, is found to be effective to increase the in-plane alignment and processing rate of buffer layers. PLD-YBCO layers on the self-epitaxial PLD-CeO2 cap layer exhibited a high degree of in-plane texturing about 3° and thus high Jc up to 4.4 MA cm−2 and high Ic of 276 A cm−1 width. Long YBCO conductor fabrication using reel-to-reel PLD equipment is now underway.

Development of TFA-MOD Process for Coated Conductors in Japan

Progresses in the development of the TFA-MOD process for the coated conductors in Japan are reviewed. In the fundamental approaches, some important advantages of Ba-poor starting solution were found such as for obtaining higher Jc, shorter reaction time and wider process temperature window. The high Ic value of 735 A/cm-w@77 K was attained. Additionally, introduction of artificial pinning centers by Sm-substitution and Zr-addition to the Ba-poor films was successfully investigated. The films showed a high minimum Ic value of 42 A/cm-w at 77 K, 1 T. Furthermore, isotropic Ic properties in the angular dependence of applied magnetic fields was realized by the uniform distribution of nanoprticles of Zr-compound. On the other hand, two different process of MOD including batch and reel-to-reel (RTR) types have been developed as an engineering process for low cost and long tape production with high superconducting performances at a high rate. In the batch type, long tape synthesis process could be developed by the optimization of the growth conditions in a large furnace. A 500 m long tape was heat-treated and a high Ic value of 310 A/cm-w in a 250 m tape was confirmed. Concerning the RTR type, a high production rate system was developed after confirmation of the ability of the continuous process in a 90 m long tape. A multi-turn with a vertical gas flow system was developed for this purpose. This system was applied to the fabrication of superconducting films on the lower cost buffer layers including a high deposition rate IBAD-MgO layer. Currently, a 5 m long tape with 250 A/cm-w was obtained at the production rate of 3 m/h using a part of the multi-turn system, which is equivalent to 15 m/h in the entire use of the furnace.

High-rate deposition of YBa2Cu3O7−δ high-temperature superconducting films by IR-laser-assisted chemical vapor deposition

We applied an infrared- (IR-) laser-assisted chemical vapor deposition technique to YBa2Cu3O7?? (YBCO) film fabrication in order to enhance the deposition rate to one suitable for commercial applications. IR-laser illumination during deposition effectively suppressed outgrowth of a-axis oriented grains, which strongly diminish the film?s current-carrying capacity. As a result, high-performance YBCO films with critical current densities of greater than 1???106?A?cm?2 were successfully obtained at high deposition rates of up to 58??m?h?1 (?1??m?min?1) by this method.