Brick-wall structure in polycrystalline TlBa₂Ca ₂Cu₃O_x thick films with high critical currents

Microstructural studies of TlBa₂Ca₂Cu ₃O_x(Tl-1223) thick films that exhibit high critical current densities (J_c) for nonepitaxial polycrystalline materials show that these films possess a]] brick-wall" structure that may be partly responsible for high current densities. The magnetic field dependence of J _c is similar to that reported for Bi-Sr-Ca-Cu-O materials that exhibit this structure. Structural analyses indicate a high degree of c-axis alignment but little in-plane texture, suggesting that high-angle [001] tilt boundaries are prevalent. Scanning and transmission electron microscopy reveal that the microstructure consists of overlapping layers reminiscent of the brick-wall structure. These results suggest that high critical current densities may be achieved by percolative transport through this structure.