LZO, a Protective Barrier Against Oxidation of NiW Alloys

Low cost Coated Conductors (CC) are required to access competitive superconducting cables. The buffer layer architecture is a key aspect of CC processing and very efficient results have been obtained with complex architecture. However, it may not be useful to have so high Jc for cable applications, and then simpler architectures have been considered. Our group has suggested in 2008 that only one buffer could be sufficient. As the deposition of YBCO needs an oxygenated atmosphere at rather high temperature, it is a key stage to study the oxygenation´seffects on the buffer layer. The aim of this study is to show results of annealing La₂Zr₂O₇/NiW substrates (LZO/NiW), with LZO deposited by MOD, under different oxygen atmospheres and conditions closed to those used in MOCVD YBCO deposition. The microstructure of the buffer layer is studied in details and tentatively related to oxidation behavior. It is shown in addition that the substrate plays in fact a crucial role, grain boundaries being the main source of oxidation. We anticipate that perhaps oxidation is an important source of degradation of critical current in YBCO.