Characterization of individual filaments extracted from a Bi-2223/Ag tape

Previous studies suggest that there is a significant variation in both shape and physical properties from filament to filament in a multifilament superconducting Bi-2223/Ag tape. We are investigating this variation for a tape with a high critical current density (J_c). For this study, we extracted all the filaments from a specially prepared high-quality tape having J_c (0 T, 77 K) = 45 kA/cm² with 19 disconnected filaments. By attaching current leads and voltage taps to the filaments, we are able to measure electrical properties on a scale of 200-300 μm. The experiments show a large variation in filament properties. The conductivity of a filament at room temperature is proportional to its critical current density J_c at 77 K (self-field) and filaments with a higher transition temperature T_c do also show a higher J_c. There is also a variation in the magnetic field behavior of the filaments. SEM pictures of the filaments also show large variations. The filaments from the center of the tape, which are thinner and have a larger aspect ratio (and thus a larger silver-filament interface), show better grain alignment and fewer impurities than filaments from the edges.