Development of LPE process for fabrication of coated conductors
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Development of LPE process for fabrication of coated conductors Teruo Izumi, Natsuro Hobara, Toru Izumi, Katsuya Hasegawa, Masahiko Kai, Hiroshi Fuji, Tetsuji Honjo, Yao Xin, Christian Krauns, Maxim Kuznetsov, Yuichi Nakamura and Yuh Shiohara Superconductivity Research Laboratory, ISTEC, Shinonome 1-10-13, Koto-ku, Tokyo 135-0062, JAPAN ABSTRACT 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 PPLQZDVFRQILUPHGHYHQZLWKRXWURWDWLRQXVLQJWKHORQJWDSHDSSDUDWXs. INTRODUCTION Through over ten years from the discovery of high Tc superconductors in 1986[1], lots of applications using high Tc superconducting materials recently have been considered and tried to fabricate. Concerning the tape application, Bi-system superconductors have been ahead for application using Ag-sheath type tapes. However, the coated conductor of RE-system superconductors (RE; Rare Earth Elements), such as the YBa2Cu3Oy phase (Y123), recently has been expected instead of the Bi-system tape because of its better performance in high magnetic fields at relatively high temperature such as 77K. Several kinds of processing have been tried to fabricate the coated conductors [2,3]. For tape application, the fabrication of the superconducting layer on a metal tape is considered to realize long tape application. On the other hand, a thick superconducting layer with high Jc to realize high Je(engineering Jc). The Liquid Phase Epitaxy (LPE) process is suitable to fabricate thick films with high crystallinity at high growth rate [4-7]. However, the solvent in the LPE process for RE123 growth is very reactive with most metals except with silver due to its high temperature of the process. Then, in our previous work, it was found that the combination of MgO or NiO buffer layer and MgO- or NiO–saturated liquid can avoid the reaction, respectively. However, the LPE film grown from the saturated liquid reveals relatively a low Tc value, which is caused by substitution of Mg for the Cu-site in the Y123 phase. In order to obtain higher Tc and Jc values, a further LPE layer without MgO or NiO (2nd LPE layer) on the substituted layer (1st LPE layer) is required. Actually, the abilities of this constructions were confirmed by the films grown on MgO single crystals. Additio
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