CRITICAL-CURRENT DENSITY NORMAL TO THE TAPE PLANE AND CURRENT-TRANSFER LENGTH OF (BI,PB)(2)SR2CA2CU3O10 SILVER-SHEATHED TAPES

We have measured the critical current density parallel (j(c)) and norm al (jc(n)) to the plane of monofilamentary (Bi,Pb)(2)Sr2Ca2Cu3O10 silv er-sheathed tapes prepared on the laboratory scale (l less than or equ al to 10 m) by the powder-in-tube technique with rolling as the only t ape-forming process. For the range of critical current densities along the tape j(c)(T = 77 K, B = 0 T)= 20...30 kA/cm(2) we obtain j(c)(n) = 2...3 kA/cm(2) normal to the tape plane. We have also directly measu red the current-transfer length L(c), i.e. the length along the tape t hat is necessary for the distribution of the current over the filament cross-section. As an upper limit we find L(c) less than or equal to 2 mm at T = 77 K for tapes with j(c)(T = 77 K, B = 0 T) > 20 kA/cm(2). Transmission electron microscopy of the polycrystalline (Bi,Pb)(2)Sr2C a2Cu3O10 filament confirms the dominant role of the frequent small-ang le c-axis tilt grain boundaries (''railway switches'') for the current transport, and the observed low anisotropy ratio j(c)/j(c)(n) approxi mate to 10 as well as the magnetic-field dependence j(c)(n)(B) agree w ell with the ''railway-switch'' model.