Abstract
YBa2Cu3O7-x oxide superconductor has intrinsically strong pinning properties at 77K, which suggests its potential for applications at liquid nitrogen temperatures. Formerly, YBa2Cu3O7-x was considered difficult for use in forming conductors because its severe intergranular weak links could not be easily removed due to difficulty in crystalline alignment control. In recent years several possibilities of using flexible coated conductor have been indicated with the effective removal of intergranular weak links to produce “biaxially aligned structures.” Four kinds of methods have been proposed to produce “biaxially aligned structures, ” such as ion-beam-assisted deposition (IBAD), modified bias sputtering, inclined pulsed laser deposition, and rolling assisted biaxially textured substrates (RABiTS). This article reviews the current status of the development of YBa2Cu3O7-x oxide superconducting tapes produced by vapor phase deposition. Biaxially aligned YBa2Cu3O7-x coated conductors have the following advantages: (a) high Jc values: stable Jc values over 105A/cm2 (77K, 0T) were achieved, and Jc values over 106A/cm2 (77K, 0T) were obtained in short samples; (b) the possibility of large-current conductors: Ic (77K, 0T) values over 100A were obtained in 2-μm-thick YBa2Cu3O7-x films; (c) strong pinning properties at 77K; (d) excellent flexibility and mechanical durability; and (e) the low a.c. losses caused by thin-strip geometry and the low conductivity of substrates. YBa2Cu3O7-x tape conductors are unexplored technologies which require long-length, flexible tapes with uniform biaxial texturing. It has been a great challenge to remove the intergranular weak links and derive the intrinsic performance of oxide superconductors, which deserves further persistent research & development.
