ALTERNATING-CURRENT ELECTRODEPOSITION (METAFUSE) PROCESS FOR FORMING THALLIUM-OXIDE SUPERCONDUCTORS

Thallium-free precursor films with the composition Ba2Ca2Cu3Ag0.37Ox (BCCO-Ag) were prepared on Ag foil by an alternating current electrodeposition (Metafuse) [A. Joseph, US Patent No. 4,764,654 (1988); No. 4,840,711 (1989)] process. The results show that the metafuse deposition process is fully capable of synthesizing controlled 223 stoichiometric films at various thicknesses (1-12 microns). The deposited precursor films were processed using a two-zone thallination furnace, which employs a Tl source zone and a separate sample zone, both within a controlled O-2 ambient environment. After thallination, the films were predominantly c-axis oriented TlBa2Ca2Cu3Oy (1223) phase. The resistive transition for a representative film is fairly sharp, with an onset temperature of 118 K and a zero-resistance temperature of 110 K. At 77 K and self-field, the critical current densities of the 2 mu m, 4 mu m and 12 mu m films were 1.96 X 10(4) A/cm(2), 1.66 X 10(4) A/cm(2), and 1 x 10(4) A/cm(2), respectively.