Current flow in yttrium barium copper oxygen deformation textured coated conductors

The current flow in YBa₂Cu₃O_7−x deformation textured coated conductors is examined on a local scale using multiple techniques. YBa₂Cu₃O_7−x coated conductors are desired for high current, high field, and low loss applications across many different industries. In this thesis, it is discovered that current does not flow uniformly in these conductors, but rather percolates through a network of grains and grain boundaries introduced into the YBa₂Cu ₃O_7−x layer by the polycrystalline substrates used.; Current percolation is demonstrated using magneto-optical imaging and local transport (voltage-current) measurements. Magneto-optical imaging is used to visualize the magnetic field above the surface of the conductors in the superconducting state. Under an applied magnetic field, magneto-optical imaging reveals that the vast majority of grain boundaries in these conductors have a critical current density less than that of the intra-grain. Magneto-optical imaging of the self-field produced by application of a transport current demonstrates that the critical current densities of the conductors are being limited in highly localized regions, by only a small subset of existing grain boundaries. Local transport measurements were conducted within individual substrate grains and across individual substrate grain boundaries. Intra-grain transport measurements reveal critical current densities exceeding 5 MA/cm 2, while most coated conductor samples have critical current densities of ∼1 MA/cm2. Transport measurements across many individual GBs exhibit a critical current density much less than the intra-grain, demonstrating again that the grain boundaries are responsible for limiting the critical current of YBa₂Cu₃O_7−x deformation textured coated conductors. Any commercial manufacturing process for YBa ₂Cu₃O_7−x coated conductors must directly address these issues.