| Bismuth cuprate high temperature superconductors are currently the only ceramic material that can be successfully processed in kilometer length wires. Bismuth cuprates form three compositions that can be represented with the generic formula Bi2Sr2CanCun+1O 8+d n = 0, 1, 2 (with critical temperatures Tc = 20K, 85-94K and 110K respectively). With critical temperatures above 77K (liquid nitrogen boiling point) the only property inhibiting a widespread use is the infield performance, that is, insufficient critical current densities in high magnetic fields. The infield critical current is intimately related to the pinning of the flux vortices that form under the influence of a magnetic field. The intrinsic pinning of flux vortices, is still not well understood in these quaternary systems. The influence of SrCuO2 second phase additions as well as internal cation nonstoichiometry was investigated as a viable way to control the flux pinning properties in the Bi2Sr2CaCu 2O8+d (Bi-2212) system. The compositions of Bi2Sr 2+xCaCu2+xO8+y (x = 0.0001-0.6) as well as Nd substituted Ca samples were prepared via freeze-drying. Phase pure stoichiometric Bi-2212 was synthesized via freeze-drying in a reduced oxygen atmosphere. It was further determined that up to 20mol% additions of SrCuO2 can be accommodated in the Bi-2212 structure and that the additions increase critical current. The incorporation of SrCuO2 into Bi-2212 results in change of both lattice parameters and modulation vector. |
