Transport Properties of Bi-2212 Bulk Superconductors prepared by Melt-Casting Process

Abstract

The Bi-2212 bulk superconductors, with a proper amount of SrSO₄, were prepared by melt-casting process (MCP). The MCP started with heating of the calcined powders at 1000°C in air until a homogeneous melt was obtained. The obtained melt was poured into a copper mold to make solid bars. The solid bars were subjected to a heating procedure at 840°C in order to reach the two-CuO layer phase. Finally, the MCP samples were annealed at 700°C in air, and rapidly quenched into liquid nitrogen, to ensure better homogeneity of the oxygen concentration. The SEM analysis of fracture surfaces reveals that the BSCCO grains are plate-like with an apparent length of about 50 μm. Critical current in bulk Bi2212 bar (φ10.7mm) exceeded 50A at 77K in self field. The weak links have been largely eliminated in the MCP sample, and the zero resistance is observed above 80K. A significant enhancement of transport properties in Bi-2212 bulk superconductors has been achieved using MCP. The AC loss value is about one-half of the theoretical value obtained by the theory of Norris. This is attributed to the inhomogeneous J_c distribution along a radial direction in the sample.