Journal of the American Ceramic Society, Vol.86, No.2, 257-265, 2003
Reel-to-reel continuous chemical solution deposition of epitaxial Gd2O3 buffer layers on biaxially textured metal tapes for the fabrication of YBa2CU3O7-delta coated conductors
A nonvacumn 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% H,) atmosphere at temperatures between 1100degrees and 1150degreesC; 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 X 10(6) A/cm(2) 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 I 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 x 10(5) A/cm(2) 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.