MOD Buffer/YBCO Approach to Fabricate Low-Cost Second Generation HTS Wires

The metal organic deposition (MOD) of buffer layers on RABiTS substrates is considered a potential, low-cost approach to manufacturing high performance Second Generation (2G) high temperature superconducting (HTS) wires. The typical architecture used by American Superconductor in their 2G HTS wire consists of a Ni-W (5 at.%) substrate with a reactively sputtered Y₂O₃ seed layer, YSZ barrier layer and a CeO₂ cap layer. This architecture supports critical currents of over 300 A/cm-width (77 K, self-field) with 0.8 mum YBCO films deposited by the TFA-MOD process. The main challenge in the development of the MOD buffers is to match or exceed the performance of the standard vacuum deposited buffer architecture. We have recently shown that the texture and properties of MOD - La₂Zr₂O_gamma (LZO) barrier layers can be improved by inserting a thin sputtered Y₂O₃ seed layer and prepared MOD deposited LZO layers followed by MOD or RF sputtered CeO₂ cap layers that support MOD-YBCO films with Ic´s of 200 and 255 A/cm-width, respectively. Detailed X-ray and microstructural characterizations indicated that MOD - CeO₂ cap reacted completely with MOD YBCO to form BaCeOs. However, sputtered CeO₂ cap/MOD YBCO interface remains clean. By further optimizing the coating conditions and reducing the heat-treatment temperatures, we have demonstrated an Ic of 336 A/cm with improved LZO layers and sputtered CeO₂ cap and exceeded the performance of that of standard vacuum deposited buffers.