Superconducting tapes with critical current density of 10/sup 4/ A/cm/sup 2/ at 77 K and zero magnetic field

Abstract

Critical current density above lo4 A/cm2 at 77 K and zero magnetic field have been achieved for both ~~a2~u306.8 '(YBCO) thin films on metallic substrates and Bi-based superconducting films on silver tapes. A transition buffer, consisting of sub-buffers deposited at different temperatures, was used to enhance the crystallinity and the transport properties' of YBCO films on metallic substrates. YBCO films were fabricated, using in-situ laser deposition, and they were strongly c-axis oriented. Critical temperature of 87 K and critical current density of 3x104 A/& at 77 K were obtained for a 0.5 mthick YBCO film. Also, the magnetic field dependence of Jc could be increased by using Pt-coated metallic substrates. For 10-20 pm-thick Bi-based superconducting tape, by using brush-on technique and heat treatment, critical current of lo4 A/cm2 at 77 K was obtained. This tape showed strong magnetic flux pinning at low temperature. The Bi-based thin films by laser deposition still suffered by the high temperature post-annealing.