THE CURRENT-CARRYING ANISOTROPY AND THE EFFECTS ON IT OF THERMOMECHANICAL TREATMENTS FOR AG-SHEATHED BI(PB)-SR-CA-CU-O SUPERCONDUCTING TAPES

The anisotropy of the current-carrying behaviours and the effects on i t of thermomechanical treatment were investigated for Ag-sheathed Bi(P b)-Sr-Ca-Cu-O superconducting tapes using DC transport electric and ma gnetic measurements. With thermomechanical treatments, the transport c ritical current density J(ct) and irreversible moment Delta m and thei r anisotropy with respect to theta (the angle between magnetic field a nd the normal of the tape surface) increase. This is attributed to the increase of the intergrain critical current density, which is closely related to the development of the c axis texturing of BPSCCO grains. For the tape with J(ct) similar to 1.5 x 10(4) A cm(-2), the anisotrop ic behaviour of both J(ct) and J(cm) (magnetic critical current densit y) was compared. Both the I-V relation in the transport measurements a nd the magnetic moment relaxation in the magnetic measurements can be well fitted by power laws, i.e., V = Al-n and m = Bt(-p) respectively. n and 1/p are related to the flux pinning potential U-e. These indica te that U-e can be well described by U-e = U-0 In(J(c0)/J). The value of n can be fitted by n proportional to H--mu and varies with theta pe riodically. The higher J(ct), the larger the n value.