We have investigated the thickness dependence of critical current for YBa2Cu3O7-x (YBCO) film with artificial pinning centers on metallic substrate. Artificial pinning centers were introduced by the pulsed laser deposition (PLD) using YBCO target including YSZ particles. The film over 1 μm in thickness exhibited with high critical current (Ic) of 40.7A in applied magnetic field of 3T parallel to the c-axis at 77K. This value was 5 times as high as the normal YBCO film without artificial pinning centers. The large Ic enabled us to approach to a practical application in the near future. Furthermore, it was clarified that the columnar nano-structure formed in the film, we call “the bamboo structure”, was a dominant pinning center because each Jc-θ curve of all thick films formed a universal line by the normalization of Jc. In addition, it was also found that YSZ addition has an optimal concentration for pinning by the study of YSZ concentration in the film.

Our multi-plume and multi-turn (MPT) pulsed-laser deposition (PLD) has been improved to accelerate reliable and fast deposition technique of high Ic (critical current) YBCO (YBa2Cu3O7-x) layer for a long coated conductor fabrication, for we increased the number of multi-turn, from three to four, in our multi-plume and multi-turn (MPT) PLD system. This increase of the number of depositing turns achieved high deposition rate corresponded to 75 mm3/h (=1 μm-thick × 10 mm-wide × 7.5 m/h, throughout all 4 turns) for YBCO layer. This four turn (4t)-MPT-PLD also indicated a capability to combine high deposition rate and high Ic. We attained the highest Ic's of 321 A at the tape speed of 3 m/h and 340 A at tape speed of 2 m/h by 4t-MPT-PLD in 10 mm-wide and 10 cm-long samples.

Based on these results, we successfully deposited a 100 m long YBCO layer by 4t-MPT-PLD. This coated conductor had high Ic as high as 159 A, therefore, the multiplication of Ic and length exhibited high value of 15.9 kA·m.

We prepared REBa2Cu3O7- δ (RE= Gd, Sm, Dy, Er, Y) coated conductors on pulsed laser deposition (PLD) -CeO2/ion-beam assisted deposition (IBAD) – Gd2Zr2O7 (GZO) / metal tapes by the PLD method and measured the characteristics in magnetic fields. The GdBa2Cu3O7- σ (Gd-123) films showed superior characteristics than others in magnetic fields and showed weak anisotropy. Critical current density (Jc) value of the Gd-123 film was 3.87MA/cm2 at self-field and 0.19MA/cm2 at 3 T of perpendicular field to the tape surface in liquid nitrogen (77 K). Angular dependences in magnetic fields (Jc -Θ) of the Gd-123 and the SmBa2Cu3O7- σ (Sm-123) were superior to others and peaks in Jc -Θ were found also at 0 degree. The reduction ratios of Jc in Jc -Θ for the Gd-123 film and the Sm-123 film were smaller than other films. Transmission electron microscopy showed that the Gd-123 film had many stacking faults. It may be considered that this stacking faults naturally introduced by the PLD method contribute to improvement of anisotropy of Jc -Θ in the Gd-123 film.

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.

YBa2Cu3O7−y(Y123) and Nd1+xBa2−xCu3O7−y (Nd123) films were deposited by the metalorganic deposition method, and the growth mechanism of these films was investigated by high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy. The Y123 and Nd123 films were prepared by spin-coating LaAlO3 (001) and SrTiO3 (STO) (001) substrates, respectively, with solutions including trifluoroacetates. Then, the samples were heat treated at 673 K in a humid O2 gas flow to form amorphous precursor films. Finally, the precursor films were heated at higher temperatures for 0–30 min in a humid Ar/O2 gas flow and cooled rapidly from those annealing temperatures. It was found that CuO crystals with a size of 10–20 nm are segregated in the Y123 and Nd123 amorphous precursor films. In the Y123 quenched film prepared by cooling the precursor film rapidly after the heat-treatment at 1048 K for 30 min, a polycrystalline film including Y2Cu2O5, BaF2, and CuO crystals was found to be generated on the c-axis-oriented Y123 film. In contrast, in the Nd123 quenched films, (NdBa)2CuO4(Nd201) phase was found to be formed first on the surface of the STO substrate. In conclusion, the c-axis-oriented Y123 film is formed by diffusion and reaction of Y2Cu2O5, BaF2, and CuO crystals, and the Nd201 phase reacts with BaF2 and CuO crystals in a humid atmosphere to form a c-axis-oriented Nd123 film.

Initial growth features of Yba2Cu3Oy (YBCO) crystal on an MgO substrate by a liquid-phase epitaxy (LPE) process were investigated and compared with homoepitaxial growth on a YBCO substrate. The partial dissolution of the seed grains in the initial stage of the LPE growth was influenced by the crystallinity of in-plane alignment of the seed grains, which could be explained by the preferential dissolution and growth mechanism. Concurrently, the slope angle of the growth grain varied with growth time. The opposite tendency of the slope angle change between the hetero- and the homoepitaxial growth was observed and could be explained by considering the difference in the step-advancing rates on each interface. It could be understood that the formation of entrapped liquid inclusions was the combination phenomena of both the small step-advancing rate of YBCO crystal on the MgO surface and the roughening of the MgO surface due to the partial dissolution of MgO to the solution.

Twinned and detwinned Yba2Cu3O7−y (Y123) single crystals were observed by transmission electron microscopy to investigate the influences of the lattice defects on the peak effect for Y123 single crystals. Twin boundaries with the spacing of 0.2–0.5 μm were seen only in the twinned Y123 single crystals. Antiphase boundaries (APBs) along the (110)Y123 plane were observed in both twinned and 0.5h-detwinned samples, which showed the peak effect in high magnetic field over 3 T at 70 K. In contrast, APBs were not found in 100h-detwinned sample. Critical current densities of this sample were small all over the range of the applied magnetic field. In conclusion, we suggest that APBs have a significant influence on the peak effect of Y123 single crystals in the high magnetic field.

Growth of the REBa2Cu3Oy (REBCO, RE = Y, Nd) crystals on the MgO substrates by the liquid phase epitaxy (LPE) process was investigated to clarify the growth mechanism. The crystal orientation of in-plane alignment was improved during the LPE process due to the preferential dissolution and growth even from a polycrystalline seed film. The orientation of preferential growth depended on the kind of RE for the REBCO system. The phenomena could be explained by the coarsening model by introducing the difference in the interfacial energies, which were considered not only general lattice matching but the Coulomb force at the interface between the REBCO and the MgO crystals. The preferential growth model was developed, and the calculation results showed a good agreement with the experimental results.

With the addition of Sr into the NdO1.5–BaO–CuOz flux, series single crystals of Nd1+x (Ba1−ySry)2−x Cu3O7±δ solid solutions (Nd1113ss) were successfully grown by crystal pulling. The liquid composition control was of key importance for controlling the crystal composition, which led to a fundamental structure control. The tetragonal Nd1113ss structure was readily obtained, using a Ba-poor liquid, due to a higher Sr liquid solubility, or using a liquid with the Ba/Cu ratio around 0.33. On the other hand, a Ba-rich liquid could effectively suppress the Nd substitution at Ba sites. The higher Sr addition for achieving a stoichiometric Nd1113 compound was thermodynamically prohibited by (i) an inherently low Sr liquid solubility and (ii) the formation of BaSrCu2Oz phase in the flux at the temperature range for crystal growth. The liquid-solid-structure relation was studied.

YBCO films on LaAlO3and IBAD (YSZ/Hastelloy) substrate were made by TFA-MOD (metalorganic deposition using trifluoroacetate) process. Improved coating solution resulted in high Jc at 77.3K and 0T of 7 MA/cm2 and 1.7 MA/cm2 for LaAlO3 and IBAD substrates, respectively. The magnetic field dependence of Jc at 77.3K also showed superior property: 105 A/cm2 at 4T (B//c-axis) for the LaAlO3substrate and at 3T (B//c-axis)) for IBAD substrate. Furthermore, the difference in Jc between single crystal LaAlO3and IBAD was small up to 3T. The present results imply that TFA-MOD process is promising for the practical YBCO coated conductor process.

Metal organic deposition (MOD) process using metal trifluoroacetate (TFA) precursors was applied to the Nd1+XBa2−XCu3Oy (Nd123) and the Tc dependence on experimental conditions such as the oxygen partial pressure (PO2) and the substrate temperature (Ts) for annealing was investigated. Thin films grown on SrTiO3 substrates at Ts = 800°C under PO2 = 300 ppm showed a Tc value of 89 K. However, from the results of TEM-EDS measurements, the substitution values of x in the Nd123 films increased from the substrate toward the surface in the film. These experimental results could be thermodynamically explained by the following model. The basic idea of the model is that the Ba potential in the precursor decreases by coarsening of BaF2 particles during the annealing for the Nd123 crystal growth. This model predicts that the small substitution value can be obtained with a higher growth rate of the Nd123 phase under low PO2.

Recent Progress of development for coated conductors by the LPE technique was reviewed. Double layered LPE films were applied to the growth on metal substrates. In both cases of MgO- and NiO- buffers, the constructions were succeeded to grow on Hastelloy and Ni tapes, respectively. In the case of the MgO-buffer, the problem, which is the melting back of the 1st LPE layer during dipping for the growth of the 2nd LPE layer, was found. The problem was solved by means of the selection of the materials for each LPE layer to introduce the difference in the growth temperature for the 1st and the 2nd layers. The lower growth temperature for the 1st LPE layer than that for 2nd one is effective to avoid the problem. On the other hand, the double layered LPE films on Ni tapes revealed Tc of 85K. Concerning the long tape processing, the high growth rate of 1≈ was confirmed even without rotation using the long tape apparatus.

The recent achievements of critical current densities in excess of 1MA/cm2 at 77K in YBCO films deposited over appropriate bi-axially textured buffer layers/metal substrates have stimulated interest in the potential future applications of coated conductors at liquid nitrogen temperature and high magnetic fields, which are called as the next/second generation tape conductors. Several different processes for obtaining the bi-axially textured buffer layers/metal substrates as well as thicker film deposition processes and non-vacuum processes are reviewed. This paper reviews the research goals of the project including the recent development of the related research by individual research group in Japan.

This paper presents tie-lines between Pr1+xBa2−xCu3O7−δ and liquid on a PrOy –BaO–CuO ternary phase diagram at 965, 970, 975, 980, and 990 °C in air atmosphere, for which knowledge is necessary to fabricate composition controlled Pr1+xBa2−xCu3O7−δ single crystals by the solution growth method. Liquidus faces have been investigated by dipping MgO single crystal rods into the thermal equilibrium melt at various temperatures and analyzing the composition of the adhering melt by ICP. The compositions of Pr1+xBa2−xCu3O7−δ solid solution coexisting with various compositions of liquids were obtained by quantitative EPMA analysis of quenched melts. Tie-lines were calculated by applying the lever rule to these experimental data for solid compositions and liquidus faces. Furthermore, the relationships between solid solubilities and peritectic temperatures of Pr1+xBa2−xCu3O7−δ are reported.

A solidification model for Pr1+xBa2−xCu3O7−δ ternary oxides by the top seeded crystal pulling (SRL–CP: Solute Rich Liquid–Crystal Pulling) method is presented in which the composition of the grown single crystals is estimated from the starting composition in the crucible. This model involves the diffusion flux balance of each element at the growth interface in the liquid considering equilibrium tie-lines in the PrOy–BaO–CuO ternary phase diagram which have been obtained experimentally. The self-diffusion coefficient for Pr and the interdiffusivities for Ba and Cu in the liquid are used in this model because this liquid is a dilute solution for Pr. The calculated results are in good agreement with the experimental ones.

A single crystal of NdBa2Cu3O7−δ was synthesized by the Top Seeded Solution Growth method (TSSG method). Then, the crystal was heat-treated 500 °C for 400 h and then 340 °C for 200 h in a pure oxygen gas flow. This sample showed critical current density (Jc) as high as 15,000 A/cm2 under a magnetic field, of 5 T, applied along the c-axis of the crystal. Electron microscopic studies with energy dispersive x-ray spectroscopy (EDS) have revealed that the Ba/Nd ratio fluctuates between 2.0 and 0.7 with a wavelength of a few tens of nanometer. This implies that superconducting phase of Nd1.0Ba2.0Cu3O7−δ and nonsuperconducting phase of Nd1.8Ba1.2Cu3O7−δ mingle with each other, which is the ideal structure for high-Jc superconducting material.

The ytrrium solubility in Ba–Cu–O solvent with a Ba to Cu ratio of 3 to 5 was investigated under different oxygen partial pressure [P(O2) = 2, 21, 100%]. A small amount of the solution was taken out by dipping thermally equilibrated MgO single crystals, and compositions of these specimens were analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). The measurements were performed for the samples prepared in the temperature range from approximately 950 °C up to 1100 °C. The peritectic temperature of YBa2Cu3O72x (Y123) decreased with decreasing oxygen partial pressure. On the other hand, the Y123 liquidus lines do not show remarkable oxygen partial pressure dependency. Accordingly, the yttrium solubility at the peritectic temperature of Y123 under P(O2) = 100% was larger than those for the other conditions [P(O2) = 2% and 21%]. Assuming a regular solution, expressions for the solubility and the enthalpy of dissolution of Y123 and Y2BaCuO5 (Y211) were derived from classical thermodynamic calculations and found to be 289 kJ/mol at P(O2) = 0.02, 239 kJ/mol at P(O2) = 0.21 atm, 206 kJ/mol at P(O2) = 1 atm for Y123, and 105 kJ/mol at P(O2) = 0.02 atm, 88.0 kJ/mol at P(O2) = 0.21 atm, and 88.4 kJ/mol at P(O2) = 1 atm for Y211. Furthermore, the Jackson α factor of Y123 was estimated to be about 20, confirming a faceted growth nature of this crystal.

We have estimated the growth rate of the YBa2Cu3Ox crystal grown from the solution by crystal pulling, in terms of solute diffusion in the liquid with convection. The maximum growth rate deduced from the solute diffusion rate is roughly estimated to be about one order larger than the typical measured value. This implies that the driving force for the surface reaction is significantly larger when compared to the total driving force for the growth of YBa2Cu3Ox crystal in our method.

We prepared the superconducting Bi-Sr-Ca-Cu-O thin films on Y3Al5O12 (YAG) single crystal substrates by metal-organic chemical vapor deposition (MOCVD). This film of 50 nm thickness on a YAG substrate showed c-axis orientation clearly, and the zero-resistivity (Tc-zero) was achieved at 66 K. The film has the advantageous property of surface smoothness compared with the film fabricated on MgO and SrTiO3 single-crystal substrates. The surface property of the YAG substrate seems to influence the film quality.