Tape Development: Microstructure and Critical Current Densities

The formation of the textured Bi,Pb(2223) phase in mono- and multifilamentary tapes is described as a result of several reactions, involving an intermediate phase, Bi,Pb(2212), which is formed as a solid solution of the initial phase Bi(2212), the latter having a monoclinic superstructure. For Bi,Pb(2223) tapes, a direct correlation between the degree of texturing of the initial Bi(2212) grains after rolling (before reaction) and of the current carrying Bi,Pb(2223) platelets (after reaction) is shown. The difference between the critical current densities of pressed and rolled tapes is discussed by comparing the maximum applicable uniaxial pressure with the local pressure exerted by the rolls. The optimization of the complex preparation process leading to long, rolled Bi,Pb(2223) tapes is discussed. The lateral distribution of the transport critical current densities in monofilamentary Bi,Pb(2223) tapes with jc(77K,0T) = 28’000 A/cm2 shows a marked minimum at the centre and a maximum at the sides, the highest value reaching 54’000 A/cm2. At 4.2K and 14T, the same tape reached the value jc = 75’000 A/cm2.