BRICK-WALL STRUCTURE IN POLYCRYSTALLINE TLBA2CA2CU3OX THICK-FILMS WITH HIGH CRITICAL CURRENTS

Microstructural studies of TlBa2Ca2Cu3Ox(TI-1223) thick films that exh ibit high critical current densities (J(c)) for nonepitaxial polycryst alline materials show that these films possess a ''brick-wall'' struct ure that may be partly responsible for high current densities. The mag netic field dependence of J(c) is similar to that reported for Bi-Sr-C a-Cu-0 materials that exhibit this structure. Structural analyses indi cate a high degree of c-axis alignment but little in-plane texture, su ggesting that high-angle [001] tilt boundaries are prevalent. Scanning and transmission electron microscopy reveal that the microstructure c onsists of overlapping layers reminiscent of the brick-wall structure. These results suggest that high critical current densities may be ach ieved by percolative transport through this structure.