Implications of low angle YBa2Cu3O7-x bicrystal transport characteristics for coated conductor applications

Coated conductor (CC) YBa2Cu3O7-x prototypes can now be made with critical current density, J(c) (77K, 0T), values of 1 - 2 MA/cm(2) and full width ha lf maximum (FWHM) in-plane misalignments of 7 degrees - 15 degrees. In orde r to understand better the current paths in such conductors, we have measur ed extended electric field - current density (E-J) characteristics in field s of 0 - 9 T at 77 IC, comparing the data to that obtained on thin film bic rystals. We find that the E-J curves of the CC show little sign of weak cou pling. We also investigate the role sample thickness plays in intergranular high field transport by measuring E-J curves up to 8 Tesla on 7 degrees[00 1] tilt bicrystal films with thickness between 75 and 300 nm. We see that t he intergrain irreversibility field increases with thickness, much as has b een seen in single crystal samples. Magneto-optic imaging and scanning elec tron microscopy show that porosity in the YBa2Cu3O7-x layer and scratches i n the ceramic buffer layers can also control J(c). These results show that the critical current density of coated conductors is limited on several len gth scales and by several different defect types.