Implications of low angle YBa/sub 2/Cu/sub 3/O/sub 7-x/ bicrystal transport characteristics for coated conductor applications

Coated conductor (CC) YBa/sub 2/Cu/sub 3/O/sub 7-x/ prototypes can now be made with critical current density, J/sub c/ (77 K, 0 T), values of 1-2 MA/cm/sup 2/ and full width half maximum (FWHM) in-plane misalignments of 7/spl deg/-15/spl deg/. In order to understand better the current paths in such conductors, we have measured extended electric field-current density (E-J) characteristics in fields of 0-9 T at 77 K, comparing the data to that obtained on thin film bicrystals. We find that the E-J curves of the CC show little sign of weak coupling. We also investigate the role sample thickness plays in intergranular high field transport by measuring E-J curves up to 8 Tesla on 7/spl deg/[001] tilt bicrystal films with thickness between 75 and 300 nm. We see that the intergrain irreversibility field increases with thickness, much as has been seen in single crystal samples. Magneto-optic imaging and scanning electron microscopy show that porosity in the YBa/sub 2/Cu/sub 3/O/sub 7-x/ layer and scratches in the ceramic buffer layers can also control J/sub c/. These results show that the critical current density of coated conductors is limited on several length scales and by several different defect types.