YSZ buffer layers and YBCO superconducting tapes with enhanced biaxial alignment and properties

Abstract

Commercial applications of YBa 2Cu 3O 7 (YBCO) superconducting cables require viable and scalable manufacturing processes. We have investigated the evolution of the biaxial alignment of yttria-stabilized zirconia (YSZ) buffer layers with increasing film thickness (50–900 nm) and report on a method of fabricating highly aligned YBCO tapes using a thin epitaxial YSZ buffer layer as template. The method employs magnetron and ion beam assisted deposition (IBAD) techniques followed by epitaxial growth to produce the buffer architectures IBAD-YSZ and epi-YSZ/IBAD-YSZ onto optically polished hastelloy metal substrates. Subsequent in situ deposition of YBCO films is used to determine the biaxial alignment at the surface of the buffer architecture, and to show that 100–200 nm thick epi-YSZ layers suffice to yield YBCO tapes that have enhanced biaxial alignment (Δ φ=9–10°) and high critical current densities: J c (77 K)=(1–2)×10 6 A cm −2 and J c (5 K,1 T)=8×10 6 A cm −2. Atomic force microscopy of the surface microstructure of the YSZ buffer layers and YBCO films reveals some grain coarsening in the epi-YSZ layers compared to the IBAD-YSZ layers while the YBCO tapes show significant outgrowths (∼200 nm) and large grains (800–1200 nm) that are similar to high- J c YBCO films grown on single crystal MgO(1 0 0) substrates.