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A 0.5 μm thick Gd2Zr2O7 layer was deposited by the ion-beam-assisted deposition (IBAD) method on an Ni-based alloy (Hastelloy), and subsequently a 3 μm thick CeO2 layer was coated by the pulsed-laser deposition (PLD) method. The in-plane alignment (Δφ) of the Gd2Zr2O7 layer and the CeO2 layer were 25° and 4.9°, respectively. TEM cross-sectional and plan-view specimens of the CeO2/Gd2Zr2O7 multilayer were prepared for detailed microstructural characterization. It was observed that the Gd2Zr2O7 layer has a columnar texture perpendicular to the Hastelloy tape surface. The columnar texture was composed of fine grains well aligned in the 〈0 0 1〉 direction. Therefore the boundaries of columns could not be observed clearly. In the CeO2 layer, the nucleation process of CeO2 grains on the Gd2Zr2O7 surface was strongly affected by both the orientation relationships and the microstructures of the Gd2Zr2O7 layer. As the CeO2 grains grew from the Gd2Zr2O7 surface, the in-plane alignment improved dramatically. The boundaries of CeO2 grains could be observed clearly and were identified as small angle tilt grain boundaries. [Copyright &y& Elsevier]

In order to fabricate long and high critical current coated conductors, new facilities for a continuous ion-beam assisted deposition (IBAD) and a pulsed laser deposition (PLD) were installed at SRL-Nagoya Coated Conductor Center (NCCC). We found a PLD-CeO2 cap layer deposited on an IBAD Gd–Zr-oxide (GZO) layer realized quite high grain alignment as well as much higher deposition rate than the conventional IBAD process, and we call this phenomenon “self-epitaxy”. Thus, the CeO2 cap layer enables an IBAD-buffer layer to be thinner, resulted in faster production speed than the conventional IBAD process. Using these facilities, we have accelerated the development of long coated conductors. A 105-m long IBAD tape and a 55-m long CeO2 cap layer with high grain alignment were fabricated. A high critical current density of 0.96 MA/cm2 at 77 K was obtained in the continuously deposited YBCO films with a reel-to-reel process on the self-epitaxial PLD-CeO2 capped IBAD-GZO layers as well as those in short samples. Long YBCO conductor fabrication using the reel-to-reel PLD equipments is now undergoing. [Copyright &y& Elsevier]

In order to optimize the ion beam assisted deposition (IBAD) process, we have investigated the influence of assisting ion beam currents on grain alignment as well as microstructure in Gd2Zr2O7-x (GZO) buffer films using a fixed short sample. It was found that an assisting ion beam enhanced crystallization of a film and, at the same time, resputtered the surface. It is important to balance both of the two factors for attaining a texturing. Other deposition parameters, such as the assisting ion beam voltage, the sputtering ion beam voltage and current, the substrate temperature, the target-to-substrate distance and so on, were also optimized and then a homogeneous and highly textured GZO buffer was obtained. We applied the optimal condition by a fixed short tape to a long tape fabrication. Although degradation in the in-plane grain alignment with deposition time was observed, this was solved by a multiple-coating process. Consequently, a 105-m long uniformly textured IBAD-GZO tape was successfully fabricated with a small deviation of in-plane grain alignments of the full width at half maximum in X-ray φ-scan, Δφ values of 14.1 and 15.0° at the both ends. [Copyright &y& Elsevier]

Gd2Zr2O7 films were formed by the ion-beam-assisted deposition (IBAD) method on an Ni-based alloy. Cross-sectional and plan-view specimens of the films were prepared for transmission electron microscopy investigation and microstructural characterization. The thicknesses of the Gd2Zr2O7 films were less than 1.3 μm. During initial formation of the films, tiny grains nucleated close to the Ni-based alloy, followed by gradual formation of a columnar texture composed of fine 〈0 0 1〉 aligned grains perpendicular to the Ni-based alloy interface. However, dark-field image taken under g→=(4 4 0) indicated that the in-plane mosaic spread of the columnar texture did not improve as much as the [0 0 1] tilt angle. However, examination of the Gd2Zr2O7 film surfaces revealed that the interfaces between columns were not well defined. Furthermore, a CeO2 film deposited on a 1.3 μm thick Gd2Zr2O7 film by the pulsed laser deposition (PLD) method contained less in-plane mosaic spread than the Gd2Zr2O7 film alone. PLD-CeO2/IBAD-Gd2Zr2O7 films are therefore considered promising candidates for use as buffer layers in superconductor tapes. [Copyright &y& Elsevier]

Abstract: High quality YBa2Cu3O7−δ coated conductors with a length of several hundred meters are available now. For practical applications of long tapes, non-destructive and efficient techniques for characterization are necessary. For that purpose, we installed a commercial machine. The measuring principle is that a tape is introduced into a space of an applied magnetic field and the induced current within the superconducting tape is evaluated by measuring the magnetic field distribution just above the tape surface using a Hall sensor array. The advantages of the technique are that the measurement speed is rather high, 15mm/s at maximum, and tapes are absolutely safe from damages by excessive heating. On the other hand, the estimation of the critical current is not straightforward because the issue of the calibration is not trivial. A 2D computer simulation code was developed to calculate the distribution of the induced current within the tape. In the simulation, it was assumed that the current–voltage relation of the superconductor obeys a power law. It is shown that the critical current deduced from the measurement is strongly dependent on the n-value. [Copyright &y& Elsevier]

Abstract: We have fabricated SmBa2Cu3O7−δ films and (Gd0.8Er0.2)Ba2Cu3O7−δ films on PLD-CeO2/IBAD-GZO/metal substrates and investigated the effect of thickness of the superconductor layer on J c under magnetic field (J c–B). For thin films up to about 0.5μm, the (Gd0.8Er0.2)Ba2Cu3O7−δ films showed higher J c than that of the SmBa2Cu3O7−δ under the magnetic field parallel to c-axis, and much higher J c than that of the SmBa2Cu3O7−δ under the magnetic field perpendicular to the c-axis. However, for thick films of 0.83μm, the J c–B characteristics were not so good in (Gd0.8Er0.2)Ba2Cu3O7−δ films due to the existence of a-axis oriented domains, while the SmBa2Cu3O7−δ films, in which few a-axis oriented domains were observed, showed the J c–B characteristics similar to the thinner films. [Copyright &y& Elsevier]

Abstract: We have developed YBCO coated conductors by Multiple-Stage Chemical Vapor Deposition (MS-CVD) technique, which can make YBCO layer with high deposition rate and easy to scale up by increasing the number of reactors. We confirmed that the high speed production by the twelve-stage CVD equipment, which was designed to scale up CVD process, did not affect the property of YBCO coated conductors and that the YBCO coated conductors with I c of 100 A-class could be fabricated by the high speed production of 10m/h. In order to demonstrate the advantage of the MS-CVD technique for longer YBCO coated conductors, we have also fabricated the 92-m-long YBCO conductor on an IBAD substrate. The YBCO conductor was fabricated with a tape moving at the speed of 25m/h and was deposited several times to control the thickness of the YBCO films. The end-to-end I c of the 92-m-long YBCO tape was measured by criterion of 1μV/cm and was 96A (J c of 1.9MA/cm2). We have successfully realized the fabrication of the YBCO coated conductor with the practical properties of 100A-class in I c and 100m-class in length. Recently, we have also obtained high I c of 227A (J c of 2.3MA/cm2) in a short sample of a YBCO conductor on IBAD substrates by optimization of the fabrication process. [Copyright &y& Elsevier]

Abstract: The dependence of superconducting layer thickness on the critical current characteristics was investigated in the range of 0.5–1.5μm for YBCO-coated conductors made by the PLD process. Since the dimension of the pinning is considered to be three as indicated by the pinning correlation length, it is concluded that the observed thickness dependence of the critical current density at low fields come simply from a degradation in the superconducting layer structure with increasing thickness. The irreversibility field and the n-value increase with the thickness. These dependencies are well described by the theoretical model of the flux creep and flow. [Copyright &y& Elsevier]

Abstract: Flux pinning properties of PLD-processed YBCO coated conductors deposited on IBAD substrate are investigated. The thickness of YBCO layer is changed in the range of 0.27–1.0μm. The thickness dependence of critical current density, n-value and irreversibility field are measured in a wide range of magnetic field. The results are compared with the theoretical flux creep-flow model. It is found that these pinning properties are strongly influenced by the thickness as well as the pinning strength. Optimum condition for high field application of this superconductor is discussed. [Copyright &y& Elsevier]

Abstract: Thick YBCO film were deposited by the PLD method on the self-epitaxial CeO2 buffered substrate: a CeO2 cap layer was deposited by the PLD method on Gd2Zr2O7 buffered Hastelloy tape by the IBAD method and highly texturing up to 4° was obtained. We have investigated the Δϕ, 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 CeO2 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 0.89A/cm2. [Copyright &y& Elsevier]

Abstract: A high speed deposition technique for YBCO coated conductors has been required from the viewpoint of cost reduction for second generation wire. The multiple-stage chemical vapor deposition technique was employed for making YBCO coated conductors with a high deposition rate. In our earlier research, over 2.0MA/cm2 of J c was confirmed on IBAD (PLD-CeO2/IBAD-Gd2Zr2O7/Hastelloy) substrates with a maximum deposition rate of 25m/h using the six-stage CVD system. To evaluate the availability of the multiple-stage CVD technique for making a longer YBCO tape, we have fabricated a 200m-long YBCO tape on a non-textured silver substrate. Deposition rate was 10m/h, and number of passing was two times. Total deposition time was 40h (20h×2). During the deposition of a YBCO layer, the CVD system was quite stable. J c was measured at a voltage tap interval of 10m with criterion of 1μV/cm. J c of the YBCO tape remained in the order of 104 A/cm2 due to the non-textured microstructure. However, J c distribution of the tape showed a good uniformity. A 210m-long YBCO/(Ag+IBAD) tape was also prepared. A 210m-long substrate combined with IBAD and Ag was used. I c of 60–78A was obtained on the IBAD substrates part. This result suggested that the multiple-stage CVD technique was very useful to making a long YBCO tape. [Copyright &y& Elsevier]

The multiple-stage CVD method is the promising technology, which can be realized for rapid and long formation of YBCO tape. In earlier researches, we have fabricated the six-stage CVD system, and successfully developed 100 m long YBCO tape at the deposition rate of 10 m/h. However, over 500 m long wires are required for the practical applications. In order to achieve this, we have studied the multi-coating of YBCO layer at further high-speed deposition. Five layers of YBCO tape were fabricated on roll milled non-textured Ag substrate directly. Each layer was deposited by the six-stage CVD system at deposition rate of 25 m/h. After each deposition, temperature of YBCO tape went down to room temperature. The distribution of Jc was within 25% and its value is the same as single coating one. No significant degradation of Jc was observed. From these results, it was indicated that the multiple-stage CVD system, which equips more reactors serially, is effective way for making longer YBCO tapes. [Copyright &y& Elsevier]