ABSTRACT

Soon after discovery of high-Tc (critical temperature) superconductivity in oxides in 1986 [1], worldwide efforts led to the development of oxides exhibiting superconductivity at temperatures above the boiling point of liquid nitrogen (77 K) [2-6]. Among the compounds with the highest critical temperatures are phases in the Bi-Sr-Ca-Cu-O (BSCCO) system [3,4] and phases in the Tl-Ba-Ca-Cu-0 system [5,6]. Since then, a huge number of oxidic high-Tc superconductors (HTSC) has been discovered. Nevertheless, the development of technical conductors presently mainly concentrates on BSCCO, as with this system it was for the first time possible to achieve high critical currents in polycrystalline HTSC wire material [7,8] applying the so-called "powder-in-tube" (PIT) technique. Since then, conductor performance has greatly improved, especially with respect to current carrying capacity along longer lengths of the conductor. The present worldwide efforts on BSCCO therefore concentrate on the development of technical (Bi,Pb)2Sr2Ca2Cu3O10+x (Bi-2223) thin textured tapes for application at 77 K (e.g., in electric energy technology) and at low temperatures (e.g. below 25 K in magnet technology) as well as on Bi2Sr2Ca1Cu208_|_x (Bi-2212) tapes and wires. At these low temperatures of 25 K or lower, Bi-2212 exhibits superior current carrying capacity as compared with Bi-2223 because the influence of Tc is negligible and Bi-2212 shows no sign of weak-link behavior, whereas Bi-2223 exhibits increasing weak-link limitations with decreasing temperature. Therefore, this material should be best suited for the envisaged use in very high-field superconducting magnets at about 4 K and also, for example, in laboratory-size magnets operated at, for example, 20 K using a cryocooler. This chapter deals with the technology and present status (as of the middle

of 1994) of monofilamentary and multifilamentary round Bi-2212 wires for application in magnet technology at low temperatures.