Transport properties of long monofilamentary Bi(2223) tapes

Monofilamentary Bi(2223) tapes withJ c(77 K, 0 tesla) up to 30 000 A/cm2 have been prepared by cold rolling using the powder-in-tube method. An optimization of the precursor powders has led to a higher phase purity after the reaction heat treatment. The deformation process has been optimized in order to increase the oxide density and to reduce sausaging effects on the oxide thickness. The transport properties of these tapes have been studied in a wide range of temperature (4.2K-T c) and magnetic fields (up to 28 tesla). The critical-current values at 77 K fields of 0.5 T and 1 T parallel to the tape surface are 10 000 A/cm2 and 5400 A/cm2, respectively. At 4.2 K theJ c value decreases from 1.6·105 A/cm2 at 0 T to 6·104 A/cm2 at 15 T. At fields higher than 15 tesla a very low field dependence ofJ c has been found, regardless of the tape orientation. Transport properties have also been studied by cutting small sections of the tape in order to investigate the local critical-current distribution. It has been found that, even in rolled tapes of good quality (J c (77 K, 0 T)>20000 A/cm2), theJ c distribution is homogeneous: the critical current density increases gradually from the centre of the tape to the sides, the latter exhibiting much higherJ c (46000 A/cm2) than in the centre (18000 A/cm2).