Optimization of buffer lagers on rolled-Ni substrates for high current YBCO and Tl,Bi-1223 coated conductors using ex-situ precursor approaches

High current YBa2Cu3O7-y (YBCO) and Tl0.78Bi0.22Sr1.6Ba0.4Ca2Cu3O9-y (Tl,Bi -1223) coated conductors were fabricated on Rolling-Assisted Biaxially Text ured Substrates (RABiTS) with a layer sequence of CeO2/YSZ/CeO2/Ni. The top and bottom CeO2 (Cerium oxide) lavers were deposited epitaxially on textur ed-Ni (100) substrates using reactive evaporation of Ce metal. The thicknes s of the CeO2 films was 200-400 Angstrom. The YSZ (Yttria Stabilized Zircon ia) levers were also deposited epitaxially on CeO2-buffered Ni substrates e ither by rf magnetron sputtering or e-beam evaporation The thickness of the YSZ films was typically 3000-9000 Angstrom. The e-beam CeO2 films were den se, crack-free and columnar. The microstructure of sputtered PSZ was dense and the e-beam deposited YSZ was porous. To understand the stability of the se buffer layers, the as-grown CeO2-buffered YSZ (both sputtered and e-beam )/CeO2/Ni substrates were annealed in a controlled oxygen furnace at variou s temperatures, RES studies indicate that the YSZ sputtered films were quit e stable up to 780 degrees C and 200-mTorr oxygen. For e-beam YSZ films, th ere was an indication of diffusion of oxygen through these buffers into the Ni substrate. The Tl,Bi-1223 films,were grown on all e-beam buffers using pulsed laser ablation of precursor films followed by post-annealing, The YB CO films were grown on e-beam/sputtered buffers using e-beam co-evaporated Y-BaF2-Cu precursors followed by post-annealing.