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REBa2Cu3Ox (REBCO, RE = rare earth) coated conductors (CCs) are promising as superconducting wires for high-field magnets because of their high in-field critical current density (Jc) performance and high tensile tolerance. Fujikura, Ltd., has been developing BaHfO3 (BHO)-doped EuBa2Cu3Ox (EuBCO, Eu = Europium) CCs using a hot-wall-type pulsed-laser deposition (PLD) in order to further improve the in-field performance. Although a high deposition rate in the PLD process is necessary for mass production, it has been found that the in-field performance greatly differ depending on the deposition rate. In this study, flux pinning properties of BHO-doped EuBCO CCs fabricated with different deposition rates by the hot-wall PLD on IBAD substrates were investigated in detail. From the scaling characteristics of the flux-pinning force density (Fp) curve, the BHO precipitates in a fast deposition rate REBCO film appeared to behave like random pinning centers, which was almost consistent with a result of transmission electron microscope observation. On the other hand, from a decrease of anisotropy in the magnetic field angle dependence of Jc, it was also confirmed that BHO precipitates were not completely random pinning centers, that is, it has some kind of anisotropy. Considering the critical current value per production time, it was also found that the fast deposition rate is advantageous since the REBCO layer could be thicker.

Fujikura Ltd., Chiba, Japan, has developed stable and high-throughput production techniques for REBCO coated conductors (CC) by using large-area ion-beam-assisted-deposition (IBAD), and hot-wall type pulsed-laser-deposition (PLD). Recently, we have been attempting to dope BaMO 3 (BMO, M: Zr or Hf) to REBCO layer in order to enhance in-field critical current density (J c ). In the course of optimizing deposition conditions of PLD for BaHfO 3 doped EuBCO films on IBAD templates, “high J c condition” and “high growth rate condition” were found. For samples prepared under these conditions, the magnetic field angle dependence of I c and REBCO thickness dependence were investigated. Finally, we succeeded in fabricating a 300-m-long CC with uniform I c distribution at the high-growth-rate condition. The longitudinal I c homogeneity (defined as standard deviation divided by average) at 77 K evaluated by magnetization method was 2.6%, which is comparable to nondoped conductors. Transport in-field I c for the both end points were 1756 and 1786 A/cm at 30 K, 2 T, respectively.

BaMO 3 (BMO, M: Zr or Hf)-doped REBCO-coated conductors were prepared by Hot-Wall PLD method on IBAD template. The highest J c was obtained for BaHfO 3 -doped EuBCO. Quite strong pinning force density (F p ) of 1.6 TN/m 3 was observed at 4.2 K, 15 T, for a sample deposited with growth rate of ~5 nm/s. It had strong c-axis correlated pinning at the temperature above 20 K with the matching field of ~5 T. A 45-m-long sample was formed by productive high growth rate over 20 nm/s, being consistent with commercial nondoped conductors. It had also large I c of 1687 A/cm and F p of 0.96 7 TN/m 3 was obtained at 4.2 K, 15 T. The end-to-end longitudinal Ic homogeneity (σ) at 77 K in low field was evaluated to be 2.2% by magnetization. Transport in-fields I c were also measured for the both end points at 30 K, 2 T, resulting in 1863 and 1883A/cm, respectively.

Recent development of production technique for RE123 coated conductors was reviewed, using Hot-wall PLD/ IBAD process. Lot-to-lot distributions for both average value and longitudinal uniformity of Ic at 77 K, 0 T were summarized for 127 run of 300-500-m-long 10-mm-wide CC. By optimizing hotwall PLD process parameters we found a reproducible high Jc production condition (20% enhancement in field at 20 K), less angular dependent to applied magnetic field. Furthermore, new hermetic type Cu stabilization foil configuration was developed and general mechanical properties against tensile strain, etc. were surveyed.

We have developed an ion-beam-assisted-deposition (IBAD) and a pulsed-laser-deposition (PLD) technique to produce REBa 2 Cu 3 O x (RE123, RE: rare earth) coated conductors with high performances. Distributions of critical currents ( I c ) in the longitudinal direction were improved in most wires routinely fabricated under optimized process. A typical wire showed I c of 460 A/cm at 77 K and self-field, about 200 A/cm at 65 K and 3 T and about 300 A/cm at 50 K and 5 T. In addition, further high I c values over 800 A/cm were also obtained in thick films. Finally, we succeeded in fabricating an 816.4 m long wire with end-to-end I c of 572 A/cm, corresponding to the new world record I c × L value of 466,981 Am/cm.

We have developed a characterization method for two-dimensional imaging of critical current density in coated conductors (CCs) based on scanning Hall-probe microscopy (SHPM). The distributions of the magnetic field around a sample were measured for several different conditions of external magnetic fields, and then were converted to those of the sheet current density which flowed to shield the external magnetic field or to trap the penetrated magnetic field. As a result, it was found that the amplitude of the sheet current density corresponded to that of critical current density almost in all the area of the sample except for the region where current direction changed. This indicates that we could obtain an in-plane distribution of the critical current density with a spatial resolution of around 100 μm in non-destructive manner by this method. We believe that this measurement will be a multifunctional and comprehensive characterization method for coated conductors.

We have studied a hot-wall heating system to produce GdBa 2 Cu 3 O y (GdBCO) films with large critical currents ( I c ) at a high production rate by a pulsed-laser-deposition (PLD) method. GdBCO films fabricated at a production rate of 30 m/h under the optimized conditions, especially a distance of 95 mm between the target and the substrate (T–S), exhibited high critical current densities ( J c ) of about 3 MA/cm 2 and I c over 300 A at a thickness of 1–2 μm. Furthermore, long GdBCO tapes prepared by repeated depositions at each tape-passing speed of 80 m/h showed uniform I c distribution along the longitudinal direction, because the hot-wall system enabled to stabilize temperature within a few degrees at 800 °C. A 170 m long tape with I c over 600 A was successfully fabricated at a production rate of 16 m/h using a laser power of 360 W.

We have studied two types of heating systems to produce thick GdBa2Cu3O7−X (Gd123) films with high critical current (Ic) stably at a high speed by the PLD method. Material yields of both PLD systems reached about 50–60% by optimization of evaporation condition. Hot-wall heating type (type 2) could fabricate the thicker Gd123 film with the higher Ic compared to contact heating type (type 1) and maximum Ic reached 1040 A at about 6 μm thick. Furthermore, it was estimated that type 2 could fabricate Gd123 film with an Ic of about 700 A at about twice speed compared to type 1. Finally, it was considered that the hot-wall heating type was very advantageous to prepare thick Gd123 film with high Ic at a high speed from the system structure.

We have visualized non-uniform current flow in RE123 coated conductors by using a scanning Hall-probe magnetic microscopy (SHPM). Newly developed SHPM system allows us to measure two-dimensional magnetic field distribution with high spatial resolution in micro-meter scale. Corresponding current density distribution can be obtained from the magnetic field image by solving inverted Biot–Savart’s law. One of the most important advantages of the present system is to visualize the current density distribution in practical high transport current and also in wide scanning area. For example, the system has current leads with large capacity up to 500 A, and the operating distance can be 15 cm by 15 cm with a micro-meter step distance. Using the SHPM system, we have successfully visualized current density distributions in the coated conductor, and clarified different kinds of non-uniform current flow. Those insights are very useful to identify local defects as well as non-uniform tape quality. These results indicate that the SHPM system is a powerful diagnostic tool not only to observe spatial inhomogeneities of transport property but also to understand their reason in practical coated conductors.

This paper describes a process for the fabrication of coated conductor (CC) wires, which is developed by Fujikura, and discusses their properties. These wires are composed of a buffer layer, which is formed by the ion beam assisted deposition (IBAD) technique, and a superconducting layer, which is formed by the pulsed laser deposition (PLD) process. In order to increase the I c × L which means the product of critical current ( I c ) and the length ( L ) of the CC wires the I c value and I c distribution along the length of CC wires have been improved by using a new PLD pilot plant. The I c value increases approximately linearly with the thickness of the superconducting layer, and it continues to increase up to a thickness of approximately 4 μm or 5 μm. The I c × L value of our fabricated CC wire is 176,023 Am. The I c value of a short sample is 972 A/cm. The process rate of IBAD is enhanced up to 100 m/h and that of PLD is enhanced up to 20 m/h. A 40-m long CC tape, which has an average I c of 300 A, is fabricated by the improved IBAD and PLD techniques.

We have carried out observations of current flow in processed RE123 coated conductors using a scanning Hall-probe microscope. Using this system, the position of defects and the resulting disturbed current flow could be observed. The two-dimensional current distribution in a 10-filament formed coated conductor (400 mum width and 100 mum space) was also investigated. Current sharing and the current distribution in each filament were quantitatively estimated. Furthermore, current penetration in quasi-static AC current mode was also measured.

By an IBAD/PLD method, a 500 m-length high-performance GdBa2Cu3Ox (GdBCO) coated conductor with BaZrO3 (BZO) was fabricated. End-to-end Ic of the 503.5 m tape was 349.6 A/cm at 77 K, corresponding Ic times L value of 176,023 Am. New approaches to decrease the thickness of IBAD buffer layers were developed by combination of IBAD-MgO(111) and IBAD-Gd2Zr2O7 (GZO). The maximum Jc of the GdBCO on the buffer layer was 550 A/cm. We also started to investigate IBAD-MgO(OOl) by using a large IBAD system with a 110 cm times 15 cm ion source. A 50 m-length IBAD-MgO tape with DeltaPhi of 13deg was fabricated at a 100 m/h-1 pass. Insulated REBCO wires with Cu or Ni-Cr lamination were developed using 5 mm-wide conductors sliced from 10 mm-wide IBAD/PLD tapes. Practical long insulated wires were supplied for several prototypes of motors, transformers and fault current limiters in fiscal 2007.

We have developed long Gd-123 coated conductors by ion-beam-assisted deposition (IBAD) and pulsed-laser-deposition (PLD) method. Recently, large-scale reel-to-reel apparatus with the 110 cm × 15 cm assisting ion source was introduced to IBAD system. It was enable to produce 500 m-class IBAD–Gd 2 Zr 2 O 7 (GZO) tapes with Δ ϕ of below 15° and high throughputs of 3 m/h. Furthermore, apparatus with multi-lane and laser scanning was introduced to PLD system. As a result, end to end I c of 318 A were obtained for a 201.5 m long tape, and I c × L values were 64,077 Am. Furthermore, 500 m-class deposition was carried out by improving PLD conditions. As a result, I c × L values of 112,166 Am was obtained and it’s a world record on August 2007. In the short samples, I c of over 500 A was obtained with Gd-123 thickness of 2.0 μm and over 100 A was obtained in magnetic field of 3 T, perpendicular to c -axis.

We have developed a long Y-123 coated conductors by ion-beam-assisted deposition (IBAD) and pulsed-laser-deposition (PLD) method. Now, we can routinely obtained 100 m class Y-123 tapes with over 100 A at 77 K. For power applications using Y-123 conductors, coiling and cooling techniques are important elements. From 2004, we have developed and demonstrated a solenoid type coil that is the most suitable for practical application because it has advantage such as (1) uniformity of magnetic field (2) no joint. In this paper, we describe the development of conduction-cooled HTS test coil that has 14 turn × 22 layers using 100 m Y-123 conductors. In order to use the conduction cooling system, the Y-123 conductors were stabilized for 0.1 mm thick Cu tapes and spacers between the layers consisted of aluminum nitride in the coils. In the demonstration of this coil at 30 K, 40 K, 50 K, 60 K and 77 K by cryo-cooling system, the good cooling and superconducting performances were observed. The central magnetic fields of over 1 T were successfully obtained with operating currents of over 400 A and under 40 K. Furthermore, this coil was operated on additional magnetic fields of 3 T by combination of LTS magnets. The central magnetic fields of 0.5 T were generated from the cooled HTS coils with operating current of 190 A on additional magnetic fields of 3 T by LTS magnets at 30 K. Total magnetic fields were exceeded 3.5 T at 30 K.

Four 5 mm-wide YBCO conductors with identical critical current were assembled face to face to obtain a stacked YBCO conductor. The magnetization losses without transport current, the transport losses without external magnetic field, and the total AC losses of the stacked YBCO conductor as well as a single YBCO conductor carrying various transport currents in transverse magnetic fields with various orientations were measured. The difference between the AC loss characteristics of the stacked YBCO conductor and those of the single YBCO conductor was clarified.

Three YBCO coated conductors with various critical currents, up to 189 A, were prepared. The magnetization losses without transport current and the total AC losses of the conductors carrying various transport currents in transverse magnetic fields with various orientations were measured electromagnetically to study the AC loss characteristics systematically. The measured total AC losses were compared with the numerical values using a one-dimensional FEM model

Thick YBa2Cu3O7-x (YBCO) films with high critical current density (Jc) values were deposited by pulsed-laser deposition (PLD) on Hastelloy with a textured CeO2/Gd2Zr2O7 buffer layer. Both cross-sectional and plan-view TEM specimens of the YBCO films were prepared, and then the nanostructural characterization of the films was performed by transmission electron microscopy (TEM). The YBCO films less than 1 μm thick were predominantly composed of c-axis-oriented grains, however, many a-axis-oriented grains, which grew larger with the increase of the thickness of the YBCO film, were formed beyond about 1 μm from the CeO2 interface. We found Y2O3 and copper oxides between a- and c-axes-oriented grains. In particular, Y2O3 grains were formed between the {001} plane of an a-axis-oriented grain and the {100} or {010} plane of a c-axis-oriented grain. The orientation relationships between Y2O3 and YBCO are found to be; (001)YBCO//(001)Y2O3 and (100)YBCO//(110)Y2O3. In addition, we also found gaps between YBCO grains. Since a-axis-oriented grain growth and the formation of Y2O3, copper oxides and the gaps are considered to reduce the J c values of the YBCO film, it is important to determine the optimum process conditions to suppress the nucleation of a-axis-oriented grains, impurity oxides and gaps.

We investigated the local inhomogeneity of flux flow dissipation by use of low temperature scanning laser microscopy (LTSLM) in a Y 1 Ba 2 Cu 3 O 7− δ (YBCO) coated conductor obtained by the Metal-Organic Deposition process using metal trifuluoroacetate (TFA-MOD process). The LTSLM images showed that the highest J c value in local region reached almost two times higher than the minimum value, while the global J c was limited by the weakest spot. Typical length scale of the spatial inhomogeneity of J c was about several tens to hundreds μm.

The texture evolution property of Gd 2 Zr 2 O 7 (GZO) template films on non-textured Ni-based alloy was studied by off-normal ion-beam-assisted deposition (IBAD) at low temperature of 200 °C, with varied bombarding ion elements of Ar, Ne, and O. In all cases a 〈1 1 1〉 axis aligned toward the ion incident direction preserving out-of-plane (1 0 0) alignment. The in-plane mosaic spread (Δ ϕ ) were clearly deteriorated for GZO films formed with assisting ions of Ar + Ne mixture or pure oxygen, compared to the case for pure Ar ion assisting. On the other hand, no recognizable ion elemental dependence on Δ ϕ was observed when GZO films were homoepitaxially grown by IBAD on already textured GZO surface.

Three types of YBCO films were deposited on metal tapes with biaxially textured CeO 2 /Gd 2 Zr 2 O 7 multilayer. One YBCO film 4 μm in thickness was formed by pulsed-laser deposition (PLD) on the stationary substrate and another film 3 μm in thickness by PLD using a reel-to-reel substrate tape transferring system. I c values of the films were 173 A and 293 A, respectively A further film 1 μm in thickness was fabricated by multiple-stage chemical vapor deposition (MSCVD). The I c value of the MSCVD-YBCO film was 100 A. The microstructures of these YBCO films were characterized using transmission electron microscopy (TEM). In the PLD-YBCO films, the films less than 1 μm thick were predominantly composed of c -axis oriented grains which were considered to grow spirally, however, irregular instances of a -axis oriented grains were also found. The a -axis oriented grains size increased with increasing thickness of the YBCO films. In the 4 μm-thick PLD-YBCO film with an I c value of 173 A, a -axis oriented grains were considered to nucleate on the CeO 2 . We found many Y 2 O 3 and cupper oxides at the boundaries between a - and c -axes oriented grains and the orientation relationships between YBCO and Y 2 O 3 were determined to be as follows: (0 0 1)YBCO//(0 0 1)Y 2 O 3 and (1 0 0)YBCO//(1 1 0)Y 2 O 3 . We also found many gaps and pores between YBCO grains. Nucleation of a -axis oriented grains was completely suppressed on the CeO 2 in the 3 μm-thick PLD-YBCO film with an I c value of 293 A. In the MSCVD-YBCO film, the YBCO film mostly consisted of c -axis oriented grains, however a -axis oriented grains and polycrystal also formed in the film. As the MSCVD-YBCO film became thicker, the a -axis oriented grains grew large, as same as in the PLD-YBCO films. The growth rate of a -axis oriented grain along the substrate normal was much higher than that of c -axis oriented grains in comparison to the difference in the growth rate between a - and c -axes oriented grains in the PLD-YBCO. In these specimens, the grain growth of the a -axis oriented grains was considered to be one of the most significant causes of degradation of J c values in the YBCO films.

We investigated the dependence of critical current, Ic, of YBCO tapes on the mechanical bending strain in order to apply them to solenoid and pancake type magnets. The tensile and compressive bending strains were applied to the YBCO tapes. The thickness of the YBCO layer on the CeO2 and Y2O3 buffer layers was 0.5 and 1.0 μm, respectively. The Ag cap layer has thickness of 10, 20, and 30 μm respectively. In every sample, no degradation of the normalized critical current, Ic/Ic0, was observed up to the first tensile and compressive strains of approximately 0.4% and 0.5%, respectively. The strain property of the YBCO tapes that were deposited with the 20 and 30 μm thick Ag cap layers showed an improvement over the tape that was deposited with the 10 μm thick Ag cap layer in terms of the tensile and compressive strains of approximately 0.5% and 0.6%, respectively. Cracks were observed on the YBCO film surface under a tensile bending strain of over 0.5%. The generation of the crack appears to be the primary reason for the Ic/Ic0 degradation. The heat cycle test was performed 10 times by applying the tensile strains of approximately 0%, 0.3% and 0.5%. The degradation of Ic/Ic0 was not observed in every sample.

Long YBa2Cu3Ox (Y-123) coated tapes were produced by reel-to-reel continuous processes using Ion-Beam-Assisted Deposition (IBAD) and Pulsed-Laser-Deposition (PLD). Biaxially textured Gd2Zr2O7 buffer layers up to 255 m long were fabricated by IBAD with the production speed of 0.5–1.0 m/h. Y-123 films were formed on them by PLD with the tape speed of 1.0–4.0 m/h. A 105 m long Y-123 film was formed with the uniform thickness of 1.0 μm and the Δϕ of 3–4°. The end-to-end Ic of 126 A was achieved at 77 K, 0 T, whose I–V curve had the n-value of 28.5. The Ic times length reached 13,230 A. Another 70 m long Y-123 tape with the Ic of over 90 A (77 K, 0 T) was wound into a solenoid type magnet whose inner diameter was 60 mm. The central magnetic field of 0.082 T was obtained at 77 K, with operating current of 42 A and that of 0.27 T was obtained at 66 K, with operating current of 130 A.

Current transport characteristics in a Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) coated conductor fabricated by a trifluoroacetates-metal organic deposition (TFA-MOD) process were investigated over a wide range of temperature and magnetic field up to 25 T. Improved TFA-MOD process was successfully introduced for the better property of critical current density, J/sub c/, at high magnetic fields. The J/sub c/ and critical current, I/sub c/, values of multi-coated film with 1.2 /spl mu/m thickness and 1 cm width were 2.1 MA/cm/sup 2/ and 251 A at 77 K in self-field. Additionally, the superior J/sub c/ properties remained even at high magnetic fields over 20 T and lower temperature, e.g. J/sub c/ value at 30 K in 25 T was 1.0 MA/cm/sup 2/. The J/sub c/ value was about 2.5 times higher than those of previous TFA-MOD process at wide range of magnetic field. Moreover, the statistical distribution of J/sub c/ in the conductor was also estimated within a framework of the percolation model. The uniformity in the YBCO coated conductor was improved by optimizing the TFA-MOD process.

Long length Y-123 superconducting tapes were produced by reel-to-reel continuous vacuum processing, by using Ion-Beam-Assisted Deposition (IBAD) and Pulsed-Laser-Deposition (PLD). Biaxially textured Gd/sub 2/Zr/sub 2/O/sub 7/ buffer layers up to 255-m long were fabricated by IBAD with production speed of 0.5-1.0 m/h. Y-123 films were formed on them by PLD with production speed of 1.0-4.0 m/h. A 105-m long Y-123 film was fabricated with uniform thickness of 1.0 /spl mu/m and /spl Delta//spl phi/ of 3-4/spl deg/. I/sub c/ of 126 A was obtained in end-to-end at 77 K, 0 T, whose I-V curve had n-value of 28.5. I/sub c/ times length reached 13,230 Am. Another 70-m long Y-123 tape with I/sub c/ over 90 A (77 K, 0 T) was wound into a Solenoid type magnet whose inner diameter was 60 mm. The central field of 0.27 T was obtained at 66 K, with operating current of 130 A.

The AC losses of YBCO coated conductors fabricated by the IBAD/PLD method were electromagnetically measured. Both the magnetization loss without transport current and the total AC loss during the simultaneous application of AC transport current and an AC external magnetic field were measured. The AC losses were numerically calculated using the one-dimensional FEM model. The magnetic field dependence and the spatial distribution of critical current density were taken into account in numerical calculations, and the calculated AC losses were compared with the measured AC losses. The critical current, the transport current, and the applied external magnetic field were varied in order to calculate the total AC loss systematically.

Spatially resolved measurements of dissipative state in YBCO coated conductors have been carried out by use of the low temperature scanning laser microscopy (LTSLM). It has been shown that the current dependent dissipation peak is well scaled by the Gaussian distribution, and its normalized distribution becomes narrower in inversely proportion to the square root of power index in the local current-voltage characteristic. From the LTSLM analysis, we can collect positional information of current limiting coordinate as well as spatial variation of local critical current. Optimizing the measurement condition, we also succeeded to visualize the dissipation even in the tape which is covered by a 10 /spl mu/m thick Ag stabilization layer.

100-m class Y-123 coated conductors were demonstrated by using reel-to-reel vacuum apparatuses of ion-beam-assisted-deposition (IBAD) and pulsed-laser-deposition (PLD). The window for Gd 2 Zr 2 O 7 deposition condition was quite wide and 100-m long IBAD-Gd 2 Zr 2 O 7 template films were routinely obtained with ΔΦ of 10° on non-textured Ni-alloy tapes. 100-m long second buffer layers of Y 2 O 3 or CeO 2 were grown by PLD on the IBAD templates with ΔΦ of 7-8°, or 5-6°, respectively. Y-123 films with ΔΦ of 7° were formed on the substrate of Y 2 O 3 //IBAD-Gd 2 Zr 2 O 7 // Hastelloy by PLD. End-to-end I c of 38 A and J c of 0.76 MA/cm 2 (77 K, self-field) were obtained in a 100-m long sample. On the other hand, ΔΦ of 3° was obtained on the substrate of CeO 2 //IBAD-Gd 2 Zr 2 O 7 //Hastelloy. J c of 2.9 MA/cm 2 were obtained in a 0.1-m long Y-123 film, and J c was improved to 1.6 MA/cm 2 for an 80-m long Y-123 tape.

The E – J characteristics were measured for a YBCO coated-conductor by using AC inductive method of third-harmonic voltage. The results are compared with the measurements obtained by the four probe method and DC relaxation method of magnetization. The results by three kinds of measurements meet approximately on a single curve and E – J curve in a wide range of electric field is obtained. Hence, the third-harmonic voltage method is useful for a continuous measurement of J c property of long coated tape. The obtained E – J characteristics are argued.

We have studied the crystalline texture improvement of the second buffer layers of Gd 2 Zr 2 O 7 and CeO 2 grown by pulsed laser deposition (PLD) on the first buffer layer of biaxially aligned Gd 2 Zr 2 O 7 film, which formed by ion-beam-assisted deposition (IBAD) with Δ φ of 10° on metal tape. The Δ φ for the second buffer layers rapidly decreased with the thickness, and reached 5° at the thickness of 1.4 and 0.8 μm, for Gd 2 Zr 2 O 7 and CeO 2 , respectively. TEM observations indicated that sharply textured second buffer layers had largely grown grains with the diameters near 1 μm. Severe contrasts in TEM from dense defect structures were observed in the initial growth stage of PLD, which gradually relaxed with the growth thickness. J C of 2.9 MA/cm 2 were obtained in a 10 cm long Y-123 film by using the sharply aligned CeO 2 second buffer layer on IBAD-Gd 2 Zr 2 O 7 template tape.

Ion-beam-assisted deposition (IBAD) has been used to prepare biaxially textured templates necessary to realizing high superconducting performance in coated conductors.The IBAD method is characterized by the direct deposition of sharply aligned templates on nontextured metal substrates using fluorite-like oxide films (yttrium-stabilized zirconia, Gd2Zr2O7, etc.).Recent progress in vacuum technology for IBAD has made it possible to reproducibly fabricate long lengths (100 m) of IBAD-GZO templates.Continuous deposition of YBCO films on these templates has been achieved by pulsed laser deposition (PLD).Furthermore, a new approach to improving the texture of IBAD templates was found by using CeO2 films grown by PLD.Trifluoroacetate-based metalorganic deposition has also been used instead of PLD to produce superconducting layers on IBAD buffered tapes, aiming at a low-cost process.This article reviews progress in the research and development of biaxially textured templates produced using IBAD and their subsequent use in fabricating superconducting tapes and wires by means of several processes.

Using an electro-magnetic method, we measured the total AC loss of a YBCO coated conductor carrying an AC transport current in an AC transverse magnetic field with various orientations. We measured the magnetization loss (energy flow from the external magnetic field) and the transport loss (energy flow from the transport current circuit) independently during simultaneous application of an AC transverse magnetic field and AC transport current. Their sum gave us the total AC loss. The transport loss increases with increasing AC transverse magnetic field, and the magnetization loss increases with increasing AC transport current. The AC transverse magnetic field and the AC self magnetic field interact with each other at the conductor edges. This nonlinear interaction is a possible cause of the increase in AC loss. Due to the high aspect ratio of YBCO coated conductors, this increase in AC loss due to the interaction between the AC transverse and AC self magnetic fields is observed even when the transverse magnetic field is nearly parallel to the conductor wide-face. When the total AC losses for various transport currents and various field orientations are plotted against a transverse magnetic field component which is perpendicular to the conductor wide-face, the plots with different field angles but identical transport current all agree quite well with each other. The total AC loss is dominated by the self magnetic field and the perpendicular component of the transverse magnetic field, both of which mostly penetrate from the conductor edges.

100 m class Y-123 coated conductors were produced by using reel-to-reel vacuum ion-beam-assisted-deposition (IBAD) and pulsed-laser-deposition (PLD) apparatuses. 100 m long IBAD-Gd2Zr2O7 template films were uniformly and routinely obtained on non-textured Ni-alloy tapes, with FWHM of Δ below 10°. Y-123 films with FWHM of Δ below 7° were formed on them by PLD. End-to-end Ic of 38 A and Jc of 0.76 MA cm−2 (77 K, self-field) were obtained in a 100 m long sample. For further texture improvement, secondary buffer layers of CeO2 and Gd2Zr2O7 grown by PLD on IBAD-Gd2Zr2O7 template films were studied. Δ of 3° and Jc of 2.9 MA cm−2 were obtained in a 0.1 m long Y-123 film and Jc improved to 1.6 MA cm−2 for an 80 m long Y-123 tape by using the CeO2 buffer layers.

We have developed 100-m class YBCO conductors using reel-to-reel vacuum apparatuses for ion-beam-assisted deposition (IBAD) and pulsed-laser deposition (PLD). IBAD-Gd2Zr2O7 films 100m long were obtained with Δφ of 10°on non-textured Hastelloy tapes. Second buffer layers of Y2O3 or CeO2 that were 100m long were grown by PLD on the IBAD templates with Δφ of 7°or 5°, respectively. YBCO films were formed on a Y2O3/Gd2Zr2O7/Hastelloy substrate using PLD. An end-to-end Ic of 38 A and Jc of 0.76 MA/cm2 (77 K, self-field) were obtained in a 100m-long sample.

It is known that the critical current density vs. field angle of an Y-123 coated tape has a broad peak around the field direction normal to the tape surface. In this work, the angular dependencies of the irreversibility field and the critical current density are analytically investigated using the flux creep-flow theory with an assumption of the angular dependence of flux pinning strength, and these results are compared with the experimental results. The angular dependence of flux pinning strength obtained so as to get a good agreement between the experimental and theoretical results suggests an existence of long pinning centers along the c-axis.

The author’s recent studies on the critical current properties in Bi-2223 multifilamentary tapes as well as YBCO coated IBAD tapes have been reviewed. Extended electric field vs. current density ( E – J ) characteristics were studied over wide range of temperature, T , magnetic field, B , and angle, θ . Based on the analysis of statistic J c distribution and scaling, we derived an analytical expression for J as a function of E , T , B , and θ . This method allows us to describe and extrapolate the nonlinear E – J characteristics even in extremely low E region and/or high B region based on rather simple measurements.

Continuous deposition of Gd 2 Zr 2 O 7 films were carried out on 10 mm width Hastelloy tapes by ion-beam-assisted deposition (IBAD). They were uniformly deposited with the in-plane mosaic spread (Δ φ ) of 10–14° in the 50 m long and of 16–18° in the 60 m long, at a production rate of 0.5–1.0 m/h. The 6 cm sample with the I c value of 141 A and the J c value of 1.25 MA/cm 2 were obtained by 6 repeated depositions using pulsed laser deposition (PLD). Continuous deposition of Y-123 films were performed by PLD on long IBAD template tapes at a tape speed of 4.0 m/h. The I c value of 40 A and the J c value of 0.8 MA/cm 2 were obtained at the length of 30 m. Furthermore, the 46 m YBCO coated tape with the I c value of 74 A and the n value of 32 was formed uniformly.

E – J characteristics in a YBCO coated conductor at low temperature and very high magnetic field up to 27 T have been estimated using experimental E – J characteristics below 12 T along with a scaling analysis based on the percolation model. 1 mm thick YBCO films was deposited on a biaxially aligned Y 2 O 3 /YSZ/Hastelloy substrate fabricated by the IBAD technique. The critical current I c for the 1 cm wide tape was 85 A at 77 K in self-field. We measured E – J characteristics in perpendicular field up to 12 T using 100 μm wide and 1 mm long bridge patterned in the tape. Statistic J c distribution and pinning properties were analyzed from the E – J characteristics. Using the pinning parameters determined by the scaling analysis, we can calculate the critical current properties as a function of temperature and magnetic field. E – J characteristics at low temperature and very high magnetic field up to 27 T were estimated analytically and compared with the experimental data. Estimated value of J c and n -value, and their error analysis were also discussed.

The E – J characteristics were measured for a YBCO-coated conductor by using the four probe method and the relaxation method of DC magnetization. The result on the latter measurement at extremely low electric fields was theoretically analyzed based on the flux creep-flow model. From the result on n -value the flux lines in YBCO are considered to be in the glass state even at high fields. The apparent pinning potential U 0 ∗ estimated from the relaxation of DC magnetization is much larger than that of Bi-2223. The present theoretical analysis clarifies a much stronger flux pinning and a higher dimensionality of YBCO in comparison with Bi-2223.

Tapes of 30-m length high-J/sub c/ Y-123 were processed by using ion-beam-assisted deposition (IBAD) and pulsed-laser deposition (PLD). Biaxially textured Gd/sub 2/Zr/sub 2/O/sub 7/ buffer layers up to 60-m length were fabricated by IBAD with production speed of 0.5 - 1.0 m/h. Y-123 films were processed on them by PLD with production speed of 1.0 - 4.0 m/h. A 30-m Y-123 film was obtained with uniform thickness of 0.5 /spl mu/m and /spl Delta//spl phi/ of 8 - 11/spl deg/. I/sub c/ of 49 A (J/sub c/ = 0.99 MA/cm/sup 2/) was obtained in 10-m length part end-to-end, whose I-V curve had high n-value of 46. The 30-m length end-to-end I/sub c/ value was 40 A (J/sub c/ = 0.8 MA/cm/sup 2/), where I/sub c/ times length reached 1200 Am.

We have investigated extended electric field-vs.-current density E-J characteristics in YBCO coated IBAD tapes. The results of a Monte-Carlo study on the depinning in a random pin medium were compared with measurements. Using a low temperature scanning laser microscope, we examined the percolative behavior of the local resistive transition in the YBCO tape. It was also shown that the depinning probability, which is proportional to the dynamic resistance of the E-J curves, is scaled as a function of reduced current density with the aid of a power index. Consequently, the E-J characteristics in the tapes can be described by the combination of the two kinds of scaling laws: one is the scaling law of the depinning probability predicted in a random network and the other is the scaling law for the flux pinning force. These properties agree well with the percolation model of depinned clusters.

Thick YBa2Cu3O7−δ (YBCO) films have been successfully formed by the liquid phase epitaxy (LPE) method on Ni–Cr alloy tape. A buffer layer of yttria stabilized zirconia and seed layer of YBCO were formed by the ion beam assisted deposition and by the pulsed laser deposition method, respectively. YBCO films have been grown from the solution of BaO–CuO–Ag–BaF2 at 820, 845 and 860 °C under low oxygen partial pressure of 2% to prevent the metallic substrate from reacting with the solution. Good YBCO films are obtained by the growth at 820 °C, and the best one shows high critical current density of 1.9 MA/cm2. A cross-sectional observation by high resolution scanning electron microscopy shows neither reaction layer nor damaged region at the substrate/YBCO film interface. θ–2θ and pole figure X-ray diffraction of the seed layer and the YBCO LPE layer show that in-plane orientation distribution is highly improved by the LPE process.

Critical current properties in a YBCO coated tape have been studied as a function of temperature, magnetic field and field angle under high magnetic field up to 18 T. 1 μm thick YBCO film was deposited on a bi-axially aligned Y 2 O 3 /YSZ/Hastelloy substrate fabricated by the IBAD technique. The value of critical current, I c , of the 1 cm wide tape reached as high as 85 A at 77 K in self-field condition. After etching the tape into 100 μm wide and 1 mm long bridge, we measured extended E – J characteristics. The value of critical current density, J c , is maintained higher than 10 5 A/cm 2 at 70 K in 5 T perpendicular to the tape surface. Moreover, the power index n and the so called glass–liquid transition field, B GL , of the tape in perpendicular field are superior to those of epitaxial film deposited on a SrTiO 3 single crystalline substrate. J c vs. angle relationship shows broad peak around 90° where field is perpendicular to the tape surface, in addition to a sharp peak at 0°. These results suggest that the tape is highly uniform and correlated defects along c -axis direction contribute to flux pinning.

Biaxially aligned growth was studied by dual-ion-beam sputtering method for ZrO 2 –RE 2 O 3 oxide films on polycrystalline Ni-based alloy substrates. Cube-textured (all axes aligned with a 〈1 0 0〉 axis substrate normal) films were obtained by low energy (∼200 eV) Ar + ion bombardment. The optimized growth temperature increased with the richer combined ratio for RE 2 O 3 . Several pyrochlore type oxides (RE 2 Zr 2 O 7 ) were found to have sharp textures at the optimized temperatures of 200 °C. The most sharply textured films were obtained for Gd 2 Zr 2 O 7 and Eu 2 Zr 2 O 7 . The time constant of texture evolution was about half compared to yttria-stabilized-zirconia. The texture sharpness degrades with the ion radius of rare-earth elements being apart from the ones for Gd, Eu.

The critical current density and the irreversibility field were measured for a coated Y-123 tape prepared by IBAD method. These results were compared with those of Y-123 thin film deposited on single crystal STO. It was found that Jc of the tape has a weaker magnetic field dependence, although its value at low fields is fairly lower than that of the thin film. This comes from the difference of the thickness. The lower Jc at low fields is due to the collective pinning property, and the better irreversibility at high fields can be attributed to a larger flux bundle volume. These results were compared with the calculated results using the flux creep-flow theory, and a good agreement was obtained. Jc was estimated with the aid of this theory assuming that a high-quality thick tape of 5 μm thick with strong pinning can be fabricated.

Continuous deposition of Gd2Zr2O7 films was carried out on 10 mm width Hastelloy tapes by ion-beam-assisted deposition (IBAD). They were uniformly deposited with the in-plane mosaic spread (Δφ) of 10–12° in the 15 m length and of 16–18° in the 60 m length, at a production rate of 1.0 m/h. In an optimized sample, Ic of 140 A and Jc of 1.2 MA/cm2 were obtained at the length of 8 cm. Continuous deposition of Y-123 films was performed by pulsed laser deposition on long IBAD template tapes at a tape speed of 1.0 m/h. Ic of 50.0 A and Jc of 0.42 MA/cm2 were obtained at the length of 9.6 m with Δφ for the Y-123 film was 9°. Furthermore, Ic of 50.0 A and Jc of 1.0 MA/cm2 were obtained in a 8 cm Y-123 sample with Δφ of 8° at a tape speed of 4.0 m/h.

Extended E – J characteristics in a YBCO coated ion beam assisted deposition tape have been studied over a wide range of perpendicular magnetic field, B , and temperature, T . The statistical distribution of the critical current density, J c , and the magnetic transition field have been analyzed within the frame work of the percolation model. It has been shown that the distribution of pinning strength in the coated tape is much sharper than that in an epitaxial thin film deposited on a SrTiO 3 single crystalline substrate. This result suggests that effective pinning sites are introduced in the coated tape. Scaling behavior of the pinning force density will also be shown. The present analysis allows us to estimate the J c value quantitatively at an arbitrary B , T and electric field criterion.

Current transport properties in YBCO coated ion beam assisted deposition tapes have been studied as a function of temperature, magnetic field and field angle under high magnetic fields up to 18 T. The value of critical current, I c , for 1 cm wide tape was 85 A at 77.3 K in self-field. Detailed properties of critical current density, J c , were studied using 100 μm wide and 1 mm long bridge patterned in the tape. The results were compared with the properties of epitaxial YBCO thin films deposited on SrTiO 3 single crystalline substrate. The value of critical current density, J c , was maintained higher than 10 5 A/cm 2 at 70 K in 5 T perpendicular to the tape surface. The value is ≈1/4 of J c value in epitaxial thin film. In higher magnetic field, the difference becomes smaller. Power E–J relationship was observed over wide range of temperature and magnetic field. The power index n were superior to those of epitaxial thin films. And, the so-called glass–liquid transition field, B GL , of the coated tape was also superior to that of epitaxial thin films. Angle dependences of J c showed a broad peak around 90° (∥ c ), in addition to a sharp peak at 0° (⊥ c ). These results suggest that correlated defects along c -axis direction contribute as pinning sites.

We have studied the hysteresis losses in YBCO tapes in magnetic fields oriented nearly parallel to their surface ( ab plane). The magnetic moment is considerably hysteretic when the applied field is oriented very close to the tape. Following an analysis published earlier [Phys. Rev. B 62 (2000) 14452], we show that the parallel-field moment is the dominant contributor to the hysteresis loss unless the c -axis component of applied field penetrates considerably. By measuring the transverse moment that is orthogonal to the applied field, we investigated the magnetic moment along the c -axis, which in other cases dominates the hysteresis loss due to the shape effect.