Rhenium and rhenium oxide as buffer layers for high T_c thin films on metallic substrates

High T_c superconductor films on metal wires for high power applications must show long-term stability. Suitable buffer layers are required to prevent interaction between the superconductor thin films and the substrate, and to improve the long-term stability. A high melting-point metal, rhenium, and its oxide, were sputter deposited on the metallic substrate, Hastelloy. The study showed that rhenium thin films were resistant to out-diffusion from the Hastelloy substrates. However, it was found that they are easily oxidized at high temperature and they are, therefore, not suitable to oxygen rich high T_c superconductors like YBCO. They might work with other types of high T_c superconductors which have a lesser oxygen dependence.