EFFECT OF OXYGEN PARTIAL AND TOTAL PRESSURES ON CRYSTALLIZATION AND CRITICAL-CURRENT DENSITY IN DOUBLE-SHEATHED BI2SR2CACU2OX SUPERCONDUCTING MULTIFILAMENTARY WIRES

Critical current densities of double-sheathed Bi2Sr2CaCu2Ox (Bi-2212) multifilamentary octagonal and round wires heat-treated in pure oxygen atmospheres or in mixed atmospheres of oxygen and nitrogen have been measured. These wires have been prepared employing ''High Oxygen Press ure Confinement Process'' in which the oxygen partial pressure is rais ed to over 0.1 MPa. The critical current density of the wire heat-trea ted in the pure oxygen atmosphere degrades with increasing oxygen pres sure. On the other hand, the critical current density in the case of h eat treatment in the mixed atmospheres is enhanced by optimizing oxyge n partial pressure, accompanied by increasing the total pressure. As a typical case, a critical current density of similar to 1.0 x 10(5) A/ cm(2) has been realized at 4.2 K in 0 T for multifilamentary round wir e of 1.04 mm in diameter. A new model for Bi-2212 crystallization is p roposed taking account of high pressure nitrogen inside the wire, whic h relatively suppresses growth rate of non-superconducting materials a nd yields a highly oriented crystalline structure.