High Jc coated conductors with a simple buffer layer architecture

Abstract

We report on the in situ route for the continuous fabrication of YBCO coated conductors (CC) by thermal co-evaporation. CC architecture consists of YBCO film grown on biaxially textured Ni-alloys tapes buffered with a single layer of CeO2. The buffer layer deposition has been optimized by either e-beam or thermal evaporation using respectively ceria or metallic cerium. Best results have been obtained on CeO2 film, with a thickness less or equal than 100nm, grown in a reducing atmosphere at 690°C with a growth rate of 2.4Å/s. The optimal samples exhibit a highly biaxial texture, as indicated by FWHM values in the range of 5–8° and 4–6° for respectively in- and out-of-plane orientations. The layers are characterized by an uniform and crack-free surface with an average roughness lower than 10nm. SIMS analysis confirms the effectiveness of CeO2 buffer layer against Ni interdiffusion. This template allows to obtain YBCO films strong textured, with good superconductive properties. YBCO texture data are equivalent the CeO2 ones. Midpoint critical temperature, Tc, falls reproducibly in 87–88K range, with transition widths ΔTc<2−3K. Critical current density, Jc, up to 2MA/cm2 at 77K in self-field, have been achieved in a meter long CC corresponding to Ic/width value of 130A/cm-width. Uniformity and reproducibility of long CC properties are under optimization.