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

We report on the in situ preparation of YBa2Cu3O7-delta films uniformly deposited over large areas, >20 x 20 cm(2), at 690degreesC 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, T-c fall reproducibly in the 87-88 K range with transition widths DeltaT(c) = 1 K. Remarkably high transport critical current densities, J(c) 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.