Phase formation and thermal treatment optimisation in uranium compound doped (Bi,Pb)2Sr2Ca2Cu3Ox/silver superconducting tapes

A combination of uranium doping with thermal neutron irradiation has been well demonstrated to be one of the most effective means to introduce pinning centres in Bi-2223/Ag tapes. A substantial improvement in flux pinning and reduction of anisotropy in uranium-doped Bi-2223/Ag tapes has been achieved due to thermal neutron irradiation. However, the radioactivity of silver sheath is too high for practical application of this technique. In the current study, a number of U-containing compounds, U3O7, UCa2O5, and UCa1.5Sr1.5O6 have been used as dopants. The compatibility and interaction between U-compound and Bi-2223 matrix was systematically studied with various thermal processing conditions. UCa1.5Sr1.5O6 shows a remarkable compatibility with Bi-2223 phase, with critical current density reduced by about 15% at a doping level of 1.1 at.%, compared with the 85% reduction in critical current density at the same doping level for pure U-oxide doping. XRD results show that UCa1.5Sr1.5O6 has no effect on Bi-2223 formation while U3O7 caused degradation of Bi-2223 phase up to 50% at doping level of 1.1 at.%. The U-compound doping also widens the processing window to 15 degreesC. (C) 2001 Elsevier Science B.V. All rights reserved.