Brick-wall structure in polycrystalline TlBa2Ca2Cu3Ox thick films with high critical currents

Abstract

Microstructural studies of TlBa₂Ca₂Cu₃O_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.