Progress on Single Buffer Layered Coated Conductors Prepared by Thermal Evaporation

Abstract

Coated conductors with a single CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> buffer layer architecture have been developed in recent years by various research groups owing to the simplicity and cost effectiveness. The main challenge of this architecture is the modest thickness (~100 nm) of crack-free CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layers. In this work, we report on the successful deposition of thicker crack-free single CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> buffer layers on biaxially textured Ni-5 at%W substrates by e-beam evaporation thanks to the use of dopants, such as Sm, Yb or Zr, introduced in pure CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> targets. We have minimized the mechanical stress at the CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /substrate interface, that is responsible for the cracking, by optimizing the dopant concentration. X-Ray diffraction rocking curve analyses show that such doped Ceria layers have a strong out-of-plane c-axis orientation with FWHM values of 5deg. Further analysis by scanning electron microscopy shows dense and crack-free layers. These results indicate no sizeable degradation of the high epitaxial quality of the layers induced by the doping. We finally report on the deposition of high-quality superconducting YBCO films on such improved single buffer layer structures using thermal co-evaporation assisted by a novel oxygenation method based on a supersonic oxygen gas beam.