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YBCO films grown by the starting solution with Ba-poor (cation ratio as Y : Ba : Cu 1 : 1.5 : 3) have been reported to have higher Jc than that for YBCO films with stoichiometric composition due to smaller and less pores in TFA-MOD YBCO. In this study, Ba concentration in the Ba-poor YBCO films was controlled in film thickness direction, and influences of the Ba concentration gradient on microstructures and Jc properties were investigated to realize higher Jc. Precursor films with Ba-poor composition and with Ba-rich composition in the thickening direction were prepared and then the films were crystallized. Increasing the Ba concentration in thickening direction led to higher Jc than that of Ba-poor YBCO. Cross sectional TEM observations showed that the effective YBCO thickness increased for YBCO film with higher Ba concentration in comparison to the previous Ba-poor YBCO film. [ABSTRACT FROM AUTHOR]

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

We have investigated the influence of the H2O vapour inlet temperature in the calcination on both the microstructure and superconducting properties of YBa2Cu3O7-x (YBCO) films fabricated by the TFA-MOD method, from the viewpoint of the process control in the reel-to-reel system. Low critical current (Ic) values were obtained in the films prepared by introducing the H2O vapour at temperatures less than 200°C. XRD measurements and cross-sectional TEM observations suggest that the YBCO films calcined with the H2O vapour inlet temperature below 200°C revealed a random orientation without the epitaxial growth of the YBCO phase grains. Consequently, it is necessary to introduce H2O vapour from temperatures higher than 250°C in calcination for fabrication of high performance YBCO tapes. In reel-to-reel system, it is important that the humidity management in a low temperature range in the furnace. [ABSTRACT FROM AUTHOR]

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The recent progress in R&D of TFA-MOD process for the coated conductors are reviewed. On the effort towards fabricating high Ic tape, a new process to prevent crack formation in the thick film, which is the intermediate annealing between calcination and crystallization steps, was developed. Additionally, control of the composition from the 123 stoichiometric ratio, especially for Ba-poor composition, is found to be effective to improve Jc values of the films. Consequently, the extremely high Ic value of 692 A was obtained. On the other hand, a reel-to-reel system has been applied to fabricate long tapes. The high Ic value of 250 A/cm-w in a 4 m long tape and the reasonable long tape of 25 m with 100 A/cm-w were obtained. Additionally, it was newly found that the humidity control to be low PH2O in the coating room is effective to suppressing the degradation of the Jc characterization. [ABSTRACT FROM AUTHOR]