Grain boundary networks in high-performance, heteroepitaxial, YBCO films on polycrystalline, cube-textured metals

Grain boundaries (GBs) in high-temperature superconductors suppress the critical current density (J_c) dramatically, with the J_c decreasing exponentially with GB angle, especially when GB misorientation exceeds 4°. To reduce the number of high-angle GBs, fabrication of biaxially textured, superconducting wires via heteroepitaxial growth on cube-textured metals has been widely investigated worldwide. Such wires exhibit very high J_c in applied magnetic fields despite having a majority of GBs with total misorientations in the range 4-8°. Here, we show that GB networks in these wires have numerous GBs with out-of-plane misorientations greater than 4° but few boundaries having in-plane misorientations greater than 4°. Transport measurements on bicrystal GBs show that GBs with out-of-plane tilts between 4° and 8° are well linked. Together, these results explain the high performance of superconducting films on cube-textured metals.