Characteristic of the flux pinning at intergrain boundaries in bulk Bi-Pb-Sr-Ca-Cu-O superconductors

The magnetization measurement shows that there are two kinds of different intergrain boundaries in the sintered Bi1.8 Pb0.34 Sr1.86 Ca2 Cu3Oy superconductors. One has nearly no pinning force for flux line, the other can trap some flux line in the low field range where a pinning current may be sustained. When the applied field is removed, most of the remanent magnetization comes from the intergrain boundaries. The area of hysteresis loop at low field and the remanent magnetization for the cold-pressed bulk samples are significantly increased. Cold pressing results in aligning the grain orientation and raising the packing density, both of which enhanced intergrain coupling. The Jc value of 1040 A/cm2 at H = 0 and 150 A/cm2 at H = 1 k Oe are obtained. The flux creep along the intergrain boundaries and the pinning potential energy U0 for the coldpressed samples are also discussed