Microstructure dependence of the c-axis critical current density in second-generation YBCO tapes

C-axis current flow in high temperature superconductor (HTS) tape-shaped wires arises in configurations where the local wire axis is not perpendicular to the local magnetic field, such as in power cables with helically wound HTS tapes. The c-axis critical current density Jcc has been recently found to be orders of magnitude lower than the ab-plane critical current density Jcab. Here we report on Jcc (77 K, sf) values of various YBa2Cu3O7-based (YBCO) tapes with different microstructures. Our results show that the value of Jcc (77 K, sf) decreases significantly with increasing concentration of ab-plane stacking faults in YBCO thin films and that the critical current anisotropy γ = Jcab/Jcc can reach values as high as 2070, implying that in the highest-anisotropy tape, ∼20% of the tape width carries c-axis current in a helically wound power cable.