Progress in Single Buffer Layer Coated Conductors prepared by Thermal Evaporation

Coated conductors with a single CeO2 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 (similar to 100 nm) of crack-free CeO2 layers. In this work, we report on the successful deposition of thicker crack-free single CeO2 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 CeO2 targets. We have minimized the mechanical stress at the CeO2/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 5 degrees. 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.