Investigation of current percolation characteristics in coated conductors

The IBAD and RABiTS coated conductors are investigated by variable temperature scanning laser microscopy (VTSLM). In 50 μm scanning step images, IBAD samples appear to have more uniform current distribution than RABiTS samples, which can be related to the smaller grain sizes in IBAD. The images of IBAD samples taken with higher resolution reveal feather-like clusters with 40-150 μm in diameter. In RABiTS, the shape and size of percolation clusters are clear and do not change between high and low resolution images, and they are estimated to be 50-150 μm. VTSLM images prove that the current percolation in the transition region is due to the combination of the grain boundary network and the critical temperature variation. At the temperature below the critical temperature, the images of VTSLM show that the current bottleneck area causes the major local dissipation limiting I_c. We also find that the dissipation areas have lower T_c^* and high δV_m, an important characteristic shared among all the lower J_c^* areas.