Reel-to-reel continuous chemical solution deposition of epitaxial Gd₂O₃ buffer layers on biaxially textured metal tapes for the fabrication of YBa₂Cu₃O_7-δ coated conductors

A nonvacuum reel-to-reel dip-coating system has been used to continuously fabricate epitaxial Gd₂O₃ buffer layers on mechanically strengthened, biaxially textured Ni-(3 at.% W-1.7 at.% Fe), defined as Ni-alloy, metal tapes. Because of its significance as a seed layer, optimum processing conditions (postannealing speed and temperature) of Gd₂O₃ buffer layers have been studied. Highly textured films were obtained under reducing (96% Ar + 4% H₂) atmosphere at temperatures between 1100° and 1150°C; postannealing speed did not significantly affect the crystalline quality of the Gd₂O₃. Scanning electron microscopy revealed a continuous, dense, and crack-free surface morphology for these dip-coated buffers. The Gd₂O₃ layer thickness led to pronounced differences in the growth characteristics of the subsequent YSZ and CeO₂ layers deposited by rf-magnetron sputtering. Epitaxial YBCO films grown by pulsed laser deposition on the short prototype CeO₂/YSZ/Gd₂O₃/Ni-(3 at.% W-1.7 at.% Fe) conductors yielded self-field critical current densities (J_c) as high as 1.2 × 10⁶ A/cm² at 77 K. Pure Ni tapes were used to assess the viability of dip-coated buffers for long length coated conductor fabrication. The YBCO films, grown on 80 cm long and 1 cm wide CeO₂/YSZ/Gd₂O₃ buffered Ni tapes by the industrially scalable ex situ BaF₂ precursor process, exhibited end-to-end self-field J_c values of 6.25 × 10⁵ A/cm² at 77 K. These results demonstrate the reproducible epitaxy of solution-derived seed layers on pure Ni and Ni-alloy tapes as well as underscore the viability of solution approaches for the production of long length YBCO-based coated conductors.