NONSUPERCONDUCTING PHASES AND THEIR INFLUENCE ON CRITICAL-CURRENT DENSITY IN AG BI2223 TAPES/

The influences of chemical composition, sintering time and temperature on J(c) through the microstructure change have been investigated for the silver sheathed Bi2223 tapes prepared by the powder-in-tube techni que. The highest J(c) was realized for the heat-treatment condition at 1109 K for longer than 700 ks, where two superconducting phases of 22 23 and 2212 coexist with three non-SC phases of Ca2PbO4, CuO and (Sr, Ca)(3)Cu5O8. In order to optimize the chemical composition, nine speci mens with different composition were examined. Three kinds of six-phas e field were found out, in which the degree of thermodynamic freedom b ecomes univariant. The total amount of non-SC phases was suggested to become minimum at the boundary among those six phase fields. Nearby an invariant reaction is predicted to take place at a temperature higher than 1109 K.