Two- and three-dimensional connectivity and current distribution in YBa2Cu3Ox-coated conductors

The microstructure of YBa2Cu3Ox (YBCO)-coated conductors depends strongly on the deposition method and thickness of the YBCO layer. This letter shows how the clear qualitative difference in grain connectivity between vacuum-deposited and solution-grown layers has direct consequences for the spatial distribution of the critical current density (Jc). Pulsed-laser-deposited YBCO conductors usually have a columnar grain structure that results in a two-dimensional current network, as demonstrated with magneto-optical imaging. Consequently, their transport Jc varies considerably on length scales from 50μm up to 5mm, with current suppression occurring even at defects that run parallel to the macroscopic current. In contrast, the thicker YBCO coatings in metalorganic-deposited samples have a layered structure, leading to a three-dimensional current path. Magneto-optically, this is deduced from sample-wide shielding currents, while transport experiments reveal much smaller spatial variations in Jc. These results are encouraging for the further development of nonvacuum produced YBCO-coated conductors, since such three-dimensional systems are inherently more “forgiving” of local defects.