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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.

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 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.

As a method of the fabrication process of YBa 2 Cu 3 O 7− x (YBCO) coated conductors, the metalorganic deposition (MOD) process using metal trifluoroacetates (TFA) has been considered to be a strong candidate as a low cost fabrication process for coated conductors with high J c . In the case of the MOD process using the TFA salts for the all three elements, it requires several tens hours in the calcination process for each single coated film to minimize the generation of pores in the film. In order to shorten the calcination time, a new combination of starting materials was developed. In this study, the new heating process for these new materials has been investigated. Consequently, the calcination time was shortened to be about 17%. Also, the overall transport I c of 292 A and the J c value of 2.0 MA/cm 2 were achieved with 1.48 μm in thickness at 77 K in self-field.

Influence of the process conditions, including the water partial pressure and the total annealing pressure, on YBa 2 Cu 3 O 7− y (YBCO) film growth has been investigated in order to increase the growth rate. YBCO films have been fabricated on SrTiO 3 substrate by metal-organic deposition using trifluoroacetates (TFA) as a solute source under the low-pressure atmosphere. It was observed that the growth rate of the YBCO film was in proportion to the square root of the water partial pressure and was in inverse proportion to the total pressure. A higher YBCO growth rate was achieved about 3 times as fast as that under the atmospheric fabrication conditions with maintaining the high J c performance. On the other hand, the volume fraction of a -axis oriented grains in the YBCO film was strongly dependent on the growth rate, a -axis oriented YBCO grains were clearly recognized in the films grown with either very low or very high growth rate. As a result, it was found that the growth region should be controlled to prevent from the growth of the a -axis oriented grains.

The recent progress in R&D of coated conductors by TFA–MOD process was reviewed. For the several targets, such as high superconducting performance, high production rate, long tape etc., the steady progresses could be recognized. The high J c and I c values of 3.6 MA/cm 2 and 291 A were achieved by using a highly aligned CeO 2 cap on an IBAD–GZO layer and optimizing the conditions in the multi-coating process, respectively. For improving the production rate, the calcination time was extremely reduced by the development of the new combination of the starting materials. As the improvement of the production rate, the process for achieving high growth rate was investigated by controlling the atmosphere conditions in the high temperature heat treatment. It was found that both high humid partial pressure and low total pressure conditions were both effective to improve the growth rate and the three times higher growth rate with maintaining high J c than that in the conventional conditions was confirmed. Additionally, a 0.25 m long tape with uniform I c values over 200 A and the end-to-end I c value of 210 A was successfully fabricated with traveling in the furnace of the Reel-to-Reel system.

YBa 2 Cu 3 O 7− δ (Y123) films were deposited under various water partial pressures ( P H 2 O ) in the crystallization process by the advanced metalorganic deposition (MOD) method using trifluoroacetates. Microstructures of the films were evaluated by means of transmission electron microscopy. As a result, in the Y123 film crystallized under lower P H 2 O such as 2.1%, large pores were remarkably observed. Furthermore, there were many amorphous layers of a non-superconducting phase in this film. In contrast, small pores were distributed in the films deposited under higher P H 2 O . Considering that the critical current ( I C ) values become higher as P H 2 O increases, existence of large pores and non-superconducting phase crystals causes to reduce I C . Through the investigation of the microstructure of the films quenched during the crystallization process, it was found that the pores in the film are generated by reaction of the non-superconducting phases, which are trapped in the growing Y123 film afterwards, to transform to Y123 with accompanied by the volume reduction of about 30%. The sizes of the entrapped phase crystals in Y123 film depend on the P H 2 O and it may determine the pore sizes in the final film.

The long tape process was developed using the advanced TFA precursor solution. In a long tape production, the advanced TFA precursor solution was coated by a die-coater using the reel-to-reel system, and the multi-coating method was applied for thicker film fabrication. We successfully fabricated long uniform precursor films. In the high temperature treatment, a large scale equipment for the continuous long tape process was developed. This equipment had a perpendicular gas flow system to the tape length which is effective to fabricate the uniform films. I c values and its distribution in the YBCO tape fabricated by this method on CeO 2 /IBAD-Gd 2 Zr 2 O 7 /Hastelloy were measured. And the uniform and high performance was confirmed. A 0.25 m long YBCO film with 1.38 μm in thickness on the metal substrate shows the high I c performance of 210 A with end to end at 77.3 K in self-fields.

Y123 precursor and final films were deposited at various heating rates in the calcination process of metal organic deposition method using trifluoroacetates. The superconducting characteristics were evaluated in the final films. The microstructures and the distributions of chemical compositions of these films were also investigated using transmission electron microscopy and energy dispersive X-ray spectroscopy. In the Y123 precursor film prepared by heating at the rate of 0.2 °C/min in the temperature range from 200 to 250 °C, Cu was distributed uniformly. On the other hand, in the precursor film prepared by heat-treating at the rate of 5 °C/min from 200 to 250 °C, Cu was found to be segregated in the vicinity of the surface of the film. This Cu segregation in the precursor film might cause the differences of crystallinity and superconducting properties of the final film. The former precursor film was grown into a c-axis oriented Y123 film with good crystallinity, and exhibited the high JC value of 2 × 106 A/cm2. However, the final film prepared by heat-treating the latter precursor film had many stacking faults of CuO planes, and showed the lower JC value of 0.3 × 106 A/cm2.

In the development for the coated conductors, the trifluoroacetates-metal organic deposition (TFA-MOD) process using the multi-coating method was applied to form thicker YBa2Cu3Oy (YBCO) films on the CeO2 buffered IBAD(Zr2Gd2O7)/Hastelloy tape. As a result, in the 5 times coated film with 1.38 μm in thickness, the Jc and Ic values achieved to be 1.5 MA/cm2 and 210 A, respectively. Then, we fabricated a 1 m long YBCO tape by the continuous reel-to-reel system. As a result, we confirmed the tape to be homogeneous by XRD analysis. Additionally, we report the theoretical analysis of YBCO growth during post-annealing in the TFA-MOD process considering both the diffusion in the gas boundary layer and the growth kinetics at the precursor/YBCO interface. This model reveals a basic idea of the growth mechanism to define the steady state growth rate, and could explain the experimental results. In addition, it predicts that the growth rate could be estimated from the partial pressure of the water vapor of the inlet gas.

As a method of the fabrication processes of YBa 2 Cu 3 O 7− x (YBCO), the metalorganic deposition (MOD) process using metal trifluoroacetete (TFA) is considered to be a strong candidate due to its low cost fabrication process for coated conductors with high J c . In our previous work, a triple coated film with 1 μm in thickness was fabricated on a CeO 2 /IBAD–YSZ layer buffered Hastelloy substrate by optimizing the condition of heat treatments such as P H 2 O in the multi-coating method [Physica C 378–381 (2002) 1013]. The J c value of 1.6 MA/cm 2 (77 K in self-field) in this film patterned 100 μm width and the I c * value of 153 A/cm-width at 77 K in self-field were achieved. In order to obtain a thicker film with high overall I c * for 1 cm width, the influence of the heat treatment conditions of P H 2 O , P O 2 , and the temperature in the MOD process was investigated. Subsequently, a 5 times coated film was obtained on a CeO 2 /IBAD–Zr 2 Gd 2 O 7 layer buffered Hastelloy substrate by optimizing the conditions of heating and dip coating. As a result, the overall transport I c value was improved to 210 A and J c value of 1.53 MA/cm 2 was obtained (77 K in self-field).

The growth rate expression in the TFA-MOD process for fabrication of coated conductors was revised according to the measurement of the growth rate using a long tape. The P (H 2 O) distribution along the gas flow-direction was calculated by the advection diffusion model. The above two outputs were combined to predict the minimum annealing time for complete reaction in the sample tape with a finite width. The prediction from the model was in good agreement with the experimental results.

The metal organic deposition (MOD) process of YBa 2 Cu 3 O 7 - x (YBCO) using metal trifluoroacetate (TFA) precursors is considered to be a strong candidate as a low cost fabrication process in coated conductors since the TFA-MOD process is a non vacuum process and can provide high J c films. In order to develop long tape conductors using this process, the influence of the gas flow direction in the heat treatment was investigated. The J c value decreases toward to leeward side in the case of the parallel gas flow condition. On the other hand, in the case of the perpendicular gas flow condition. The J c value reveals uniformity in all over the tape and the high J c level is maintained. In the case of long tape production, it was found that the perpendicular gas flow to the tape length is effective to fabricate the uniform films. It could minimize the influence of consumption of H 2 O and generation of HF gas in the up-stream area to the leeward region. The J c and I c properties and these distribution of the YBCO tape fabricated by this method on CeO 2 /IBAD-Gd 2 Zr 2 O 7 /Hastelloy is presented. Furthermore, a large scale equipment for the continues long tape process was developed based on the above findings. Consequently we have fabricated a 1 m long Y123 tape conductor by a reel to reel system. Even in the first trial, the uniform reaction for the entire length was recognized.

YBa 2 Cu 3 O 7− y (Y123) and Nd 1+ x Ba 2− x Cu 3 O 7− y (Nd123) films were deposited by metalorganic deposition (MOD) method, and investigated by transmission electron microscopy and energy dispersive X-ray spectroscopy in order to elucidate the growth mechanism of the films in the MOD process. Y123 and Nd123 films were prepared by cooling rapidly during the final heat-treatment. In the case of the Y123 quenched film, it was found that a polycrystalline film is formed over a c -axis oriented Y123 film, and that there are Y 2 Cu 2 O 5 , BaF 2 and CuO particles in the polycrystalline film. In contrast, in the Nd123 quenched film, (Nd,Ba) 2 CuO 4 phase was found to be generated on the surface of the substrate. In conclusion, we suggest that the Nd123 film is formed by a reaction of (Nd,Ba) 2 CuO 4 , BaF 2 and CuO, although the Y123 film is grown by diffusion and reaction of Y 2 Cu 2 O 5 , BaF 2 and CuO crystals.

Influence of the buffer material addition to the liquid for the YBa 2 Cu 3 O y (Y123) growth in liquid phase epitaxy (LPE) process and the suitable constructions of the LPE coated conductors were investigated for both MgO- and NiO-saturated systems. In the MgO-saturated system, influence of MgO addition to the liquid was negligible in Y-solubility in liquid and the peritectic temperature ( T p ) value. The double layered LPE films of YBa 2 Cu 3 O y layer on YBa 2 (Cu,Mg) 3 O y layer, which were grown from MgO-saturated liquid, was grown on the Hastelloy tape with an MgO buffer layer. However, the growth of the second layer was unstable. It was found that the partial melting back of the first layer during dipping of the second layer growth is the reason for the unstable growth of the second layer. The problem was solved by lowering the growth temperature for the second layer than that of first layer due to selection of RE in RE123. On the other hand, NiO-addition made T p of the Y123 phase decrease and the crystallization temperature increase. This means that the possible temperature range for stable growth of the YBa 2 (Cu,Ni) 3 O y phase becomes narrow due to NiO addition. This problem was also solved by the selection of RE element in RE123 with high T p . The double layered construction was confirmed using Y123(LPE)/Sm123-Ni(LPE)/NiO/Ni. Consequently, the suitable constructions for each system were developed.

Metal organic deposition (MOD) process using metal trifluoroacetate (TFA) precursors was applied to the NdBa 2 Cu 3 O 6+ y (Nd123) and the T c dependence of experimental conditions such as oxygen partial pressure ( P O 2 ) and substrate temperature ( T s ) for annealing was investigated. Thin films grown on single crystal SrTiO 3 at T s =800°C under P O 2 =3×10 −4 atm showed a T c0 of 89 K. However, from the results of TEM-EDS measurements, the substitution value of x in Nd 1+ x Ba 2− x Cu 3 O 6+ y increased from the substrate toward the surface in the film. These experimental results could be explained thermodynamically by the following model. The basic idea of our model is that the Ba potential is changed by coarsening of BaF 2 during the annealing for the growth. This model predicts that the small substitution value can be obtained with a higher growth rate of the Nd123 phase under low P O 2 .

Trifluoroacetate metalorganic deposition (TFA-MOD) process is expected as a low cost process for mass production of coated conductors because it is a non-vacuum process. In order to apply the technique to fabrication of coated conductors, suitable buffer layers have to be considered to achieve a high orientation of superconducting layer and prevention of the reaction with metal substrate. The combination of CeO 2 on IBAD-YSZ is considered as an effective buffer for TFA-MOD process expecting to satisfy a high acid resistivity and high crystal grain alignment. The CeO 2 buffer layer was deposited on IBAD-YSZ/Hastelloy substrates by RF magnetron sputtering. From XRD analysis, the CeO 2 buffer layer showed very good in-plane alignment on YSZ-IBAD buffer layer. In a holding time of 1 h, the suitable maximum heat treatment temperature was found to be from 750°C to 775°C for TFA-Y123 on metal substrate. The J c – B property of Y123 on CeO 2 /YSZ/Hastelloy shows the J c values of 1.4 MA/cm 2 at 77.3 K, 0 T and more than 10 5 A/cm 2 at 77.3 K, 2 T. The high performance under high magnetic field was confirmed.

We tried to apply NiO as a buffer layer to liquid phase epitaxy coated conductors on the Ni substrate. The NiO addition to the solution decreased the peritectic temperature of the Y123 and increased the crystallization temperature of the Ba–Cu–Ni–O compound. This makes it difficult to grow the Y123 single phase from the NiO-saturated solution. Instead of Y123, we selected Sm123 or Nd123 that has a higher peritectic temperature than Y123, and confirmed that Sm123 or Nd123 could be grown stably from the NiO-saturated solution. Because of its low T c value of Sm123 or Nd123 grown from the NiO-saturated solution, the (Y,Yb)123 layer should be epitaxially grown as the superconductive layer on it. Finally we succeeded in growing a Sm123 layer on a Ni substrate from the NiO-saturated solution, and confirmed the structure of NiO buffered system.

For practical applications of high-temperature superconductor tape, the high production rate of tapes is needed to reduce its cost. Recently, the long-length coated conductor with high performance has been fabricated by an ion beam assisted deposition/pulsed laser deposition (IBAD/PLD) method in Fujikura. In IBAD process, we adopted IBAD–Gd2Zr2O7 (GZO) film. The process speed of IBAD–GZO film was increased up to 5 m/h using a polished metal substrate tape. To fabricate biaxially-textured buffer layers at a higher rate, we have started to develop another structures such as (a) IBAD–GZO/IBAD–MgO (3-fold symmetry) and (b) IBAD–MgO (4-fold symmetry). In the case (a), we fabricated GdBCO/CeO2/IBAD–GZO/IBAD–MgO tape and the critical current was Ic = 550 A/cm (2.46 MA/cm2) and throughput of IBAD processes were 20 m/h. In the case (b), IBAD–MgO short samples with ΔΦ of 9°–11° were obtained at 500 m/h. The 500 m/h (10 mm width) is extremely high rate in IBAD process in the world. As long-length IBAD layer 10 m, 50 m and 100 m IBAD–MgO films were fabricated at the speed of 100 m/h. After CeO2 deposition, in-plane textures of these samples were ΔΦ of 3.7°–3.7°, 4.1°–4.9° and 4.2°–4.8°. Using some of these buffer layers, we have obtained GdBCO film with Ic = 400 A/cm (2 MA/cm2, 10 m) and Ic = 550 A/cm (2.7 MA/cm2, short sample).

Long-length and low-cost coated conductors are necessary for practical use such as motor, generator, transformer, fault current limiter, SMES and so on. For fabricating low-cost coated conductors, production speeds at each process should be faster. The structure of coated conductor we adopted, is GdBa2Cu3Oy(GdBCO)/CeO2/Gd2Zr2O7 (GZO)/metal. To make processes faster without changing such beneficial structures, we adopted another buffer layer under GZO film. At the IBAD (ion-beam-assisted deposition) process, MgO is known as one of the suitable materials to achieve high alignment with thin film thickness. We fabricated IBAD-MgO film with changing deposition rates and ion-current densities, and got two types of IBAD-MgO film. One is the film with its crystal orientation aligned to the MgO(1 1 1) parallel to the tape surface, and the other is with MgO(1 0 0). And each film has in-plane texture such that 3-fold symmetry, and 4-fold symmetry respectively in the pole figure of MgO . We performed IBAD-GZO on the 3-fold IBAD-MgO film, and got 4-fold IBAD-GZO film. In-plane textures of GZO were not so different from the ordinary IBAD-GZO film, but the thickness of the films became from 1.2 μm to 0.3 μm (1/4). And a critical current of the GdBCO film on the buffer layer was over 210 A/cm (Jc > 1.5 MA/cm2) at 77 K.

IBAD-Gd 2 Zr 2 O 7 (GZO) film was fabricated on polycrystalline Ni-based alloy tape by the IBAD-system with 110 cm × 15 cm ion source. Using long-length faraday-cup-array, effects of argon gas-flows on ion-current densities were investigated. As a result, lower gas-flow leads to higher ion-current density at the substrate in the system. Under the condition of low gas-flow, 10 m (with production speed of 5 m/h), 60 m (3 m/h) and 500 m (5 m/h)-length IBAD-GZO films were fabricated and their in-plane textures were Δ ϕ = 15°, 13° and 18°, respectively. After that, PLD-CeO 2 experiments were performed on the IBAD-GZO substrates with Δ ϕ = 15° and 13°, and then CeO 2 films with Δ ϕ = 5.5° and 5.7° were achieved with the tape-speed of 5.0 m/h and 10.0 m/h, respectively.