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

A critical current density above 10/sup 4/ A/cm/sup 2/ at 77 K and zero magnetic field has been achieved for both YBa/sub 2/Cu/sub 3/O/sub 6.8/ (YBCO) thin films on metallic substrates and Bi-based superconducting films on silver tapes. A transition buffer, consisting of subbuffers 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. A critical temperature of 87 K and a critical current density of 3*10/sup 4/ A/cm/sup 2/ at 77 K were obtained for a 0.5- mu m-thick YBCO film. The magnetic field dependence of J/sub c/ could be increased by using Pt-coated metallic substrates. For 10-20- mu m-thick Bi-based superconducting tape, by using a brush-on technique and heat treatment, a critical current of 10/sup 4/ A/cm/sup 2/ at 77 K was obtained. This tape showed strong magnetic flux pinning at low temperature.