High critical current density in YBCO coated conductors prepared by thermal co-evaporation

We report on the in situ preparation of Y Ba2Cu3O7-delta films uniformly deposited over large areas, > 20 X 20 cm2, at 690 deg C by thermal co-evaporation onto Ni-5 at.% W biaxially textured tapes buffered with e-beam evaporated CeO2. Typically, the thickness of the YBCO and CeO2 layers was 0.9 and 0.1 mum, respectively. Deposition rates were 0.2 and 2.5 nm s-1, respectively. X-ray diffraction theta-2theta Bragg-Brentano and pole figure measurements, and Nomarsky optical and SEM microscopy analysis show good biaxial texture of both layers, sharp interfaces and the absence of cracks. Midpoint critical temperatures, Tc, fall reproducibly in the 87-88 K range with transition widths DeltaTc = 1 K. Remarkably high transport critical current densities, Jc, in the 2.0-2.5 MA cm-2 range are achieved at 77 K in 1 cm long samples. The above deposition route appears to be promising for the development of long-length YBCO coated conductors thanks to the relatively low deposition temperature, the high degree of uniformity over large areas and the simple single buffer layer architecture.