ASPECTS OF THE CURRENT UNDERSTANDING OF THE SUPERCURRENT TRANSPORT IN (BI,PB)(2)SR2CA2CU3O10 SILVER-SHEATHED TAPES - THE RAILWAY-SWITCH MODEL

The ''railway-switch'' model describes the superconducting current transport in (Bi,Pb)(2)Sr2Ca2Cu3O10 silver-sheathed tapes under the basic assumption that small-angle c axis tilt grain boundaries (''railway-switch'') constitute strong intergrain links for the supercurrent in the textured filament [B. Hensel, J.-C. drivel, A. Jeremie, A. Perin, A. Pollini, and R. Flukiger, Physica C 205, 329 (1993)]. We give an overview of the model and some recent experimental results with the objective to identify the mechanisms that limit the critical current density. The measurements have been performed on monofilamentary ''powder-in-tube'' samples [j(c)(T = 77K, B = 0 T) = 20..30 kA/cm(2)] that were prepared in long lengths by rolling as the only tape-forming process. We conclude that the low intragrain critical current density j(c)(c) along the c axis (or the even lower critical current density j(c)(t) across twist boundaries or intergrowths) is the dominant limitation for the transport critical current in high-quality tapes. We discuss possible starting points for a performance improvement of the (Bi,Pb)(2)Sr2Ca2Cu3O10 silver-sheathed tapes for applications.