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 it of thermomechanical treatment were investigated for Ag-sheathed Bi(Pb)-Sr-Ca-Cu-O superconducting tapes using DC transport electric and magnetic measurements. With thermomechanical treatments, the transport critical current density J(ct) and irreversible moment Delta m and their anisotropy with respect to theta (the angle between magnetic field and 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 anisotropic behaviour of both J(ct) and J(cm) (magnetic critical current density) was compared. Both the I-V relation in the transport measurements and 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 indicate 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 periodically. The higher J(ct), the larger the n value.