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

High current YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) and Tl/sub 0.78/Bi/sub 0.22/Sr/sub 1.6/Ba/sub 0.4/Ca/sub 2/Cu/sub 3/O/sub 9-y/ (Tl,Bi-1223) coated conductors were fabricated on Rolling-Assisted Biaxially Textured Substrates (RABiTS) with a layer sequence of CeO/sub 2//YSZ/CeO/sub 2//Ni. The top and bottom CeO/sub 2/ (Cerium oxide) layers were deposited epitaxially on textured-Ni [100] substrates using reactive evaporation of Ce metal. The thickness of the CeO/sub 2/ films was 200-400 /spl Aring/. The YSZ (Yttria Stabilized Zirconia) layers were also deposited epitaxially on CeO/sub 2/-buffered Ni substrates either by rf magnetron sputtering or e-beam evaporation. The thickness of the YSZ films was typically 3000-9000 /spl Aring/. The e-beam CeO/sub 2/ films were dense, crack-free and columnar. The microstructure of sputtered YSZ was dense and the e-beam deposited YSZ was porous. To understand the stability of these buffer layers, the as-grown CeO/sub 2/-buffered YSZ (both sputtered and e-beam)/CeO/sub 2//Ni substrates were annealed in a controlled oxygen furnace at various temperatures. RBS studies indicate that the YSZ sputtered films were quite stable up to 780/spl deg/C and 200-mTorr oxygen. For e-beam YSZ films, there 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 YBCO films were grown on e-beam/sputtered buffers using e-beam co-evaporated Y-BaF/sub 2/-Cu precursors followed by post-annealing.