Improved Critical Current Densities of Coated Conductors by High Aspect Ratio Grains

The critical current density J_c is limited by the network of small angle grain boundaries in coated conductors based on biaxially textured metal substrates up to a texture dependent cross-over field. Below this cross-over field J_c can be improved by optimizing the grain boundary network. One possibility to enhance J_c at low magnetic fields is to use substrates with high aspect ratio grains. Therefore, cube textured Ni tapes micro-alloyed with silver were prepared having such an elongated grain structure with an aspect ratio of about 4. Highly textured NiO layers have been grown on these substrates using surface oxidation epitaxy (SOE). YBCO films were deposited afterwards on these substrates by pulsed laser deposition using a BaZrO₃/SrRuO₃ buffer layer architecture. Transport measurements revealed a significant enhanced J_c value along the rolling direction of the tape compared to the transverse direction. Similar results were obtained in numerical simulations based on measured EBSD texture maps.