AC SUSCEPTIBILITY WEAK-LINK CHARACTERIZATION IN THE BI-PB-CA-SR-CU-O THICK-FILMS ON (IN) AG TAPE

The thick films of the Bi-Pb-Ca-Sr-Cu-O superconductor with thickness 20 mum on (in) Ag tape have been prepared by cold rolling, pressing an d annealing at 820-830-degrees-C cycles with overal thermal treatment time of 90 h. AC susceptibility data show that intragrain T(c) is abou t 108 K, while transport supercurrents start to flow at lower temperat ures (70-102 K). The temperature dependences of the intergrain critica l current density J(c)(T) have been calculated on the base of the chi' '(T) data using the model worked out. On the J(c)(T) curves sometimes one can see a bend near 65 K, which may be explained by the existence of the second superconducting phase (2122), switching on new percolati on paths for the supercurrents below that temperature. It has been fou nd that low temperature distortion of chi''(T) and J(c)(T) curves is c onnected with cracks in the superconducting layer, the cracks restrict ing critical current flow through the film. The best films obtained ha ve J(c)(77 K) 830 and 440 A/cm2 for the films in and on Ag tape accord ingly. Additional annealing of these samples at 830-degrees-C for 50 h leads to the J(c) rising for the ''on Ag'' film up to 1200 A/cm2, but J(c) for the ''in Ag'' film remains the same. The J(c) rise for ''on Ag'' film is in accordance with decreasing of J(c) suppression by crac ks due to sintering, while for the ''in Ag'' film this process is acco mpanied with partial destruction of 2223 phase.