Magnetic properties of Bi-Pb-Sr-Ca-Cu-O fabricated by various techniques

Abstract

Abstract AC susceptibility measurements and critical current densities for Bi-based superconductors fabricated by normally sintering powder in the tube technique, hot-pressing and hot isostatic pressing, are presented and discussed. It is argued that the J c of the normally sintered sample is limited by intergrain weak links, while the J c of the mechanically deformed samples is determined primarily by flux pinning. It is shown that the pinning force density is significantly increased through mechanical deformation. For Ag-sheathed tapes and hot-pressed samples, the J c drops 80% when the magnetic field is increased from ambient earth field to 0.5 T, whereas that for the normally sintered samples decreases by two orders in a magnetic field of only 0.01 T. Dislocations may act as effective pinning centres for flux lines in HIPed samples. Uniaxial pressing produces an excellent grain alignment, which allows the crystalline anisotropy to be utilized to strengthen flux pinning. The planar defects along a - b direction may induce internal Josephson weak links leading to a reduction of the J c in the c direction, but not in a - b direction. In the a - b direction, it is believed that the planar defects provide effective pinning. Utilisation of both planar defects and crystalline anisotropy may provide a valuable route towards the goal of high critical current densities.