Progress and future prospects of research and development on coated conductors in Japan

Second generation superconducting tape made of an REBa₂Cu₃O_7-δ (RE-Ba-Cu-O) is expected to show improved magnetic field dependence and more economical production cost than that shown by the first generation one of Bi-compound tape. It consists of at least three layers: a metal layer, a buffer layer of some oxide, and a superconducting layer of RE-Ba-Cu-O. Therefore, it is called a "coated conductor." There are several choices of materials and processes when making a metal-buffer layer structure and the processing of the RE-Ba-Cu-O layer. The main difficulties in producing a long superconducting tape are that the RE-Ba-Cu-O layer grains must be in-plane aligned and any defects must not exist throughout the whole length of the tape. Several different processes to obtain the biaxially textured buffer layers or metal substrates, as well as nonvacuum process for deposition of superconducting layers and buffer layers, have been developed. At present, we have developed a coated conductor tape, 30 m in length and about 0.1 mm in thickness, by means of ion beam assisted deposition (IBAD) and pulsed laser deposition (PLD), with J_c of 0.79 MA/cm² at 77 K. This presentation will review the current status of R & D on coated conductors in Japan, which includes developments of textured metal substrates including surface-oxidation epitaxy, IBAD and inclined substrate deposition for a buffer layer, and PLD and metal organic deposition for the superconducting layer.