THE INFLUENCE OF COOLING RATE ON THE CRITICAL CURRENT DENSITY OF BSCCO-2223 Ag-SHEATHED SUPERCONDUCTOR TAPES USING POWDERS PREPARED BY CO-PRECIPITATION METHOD

Abstract

The influence of cooling rate after final reaction on the transport critical current density of Ag-sheathed Bi₂Sr₂Ca₂Cu₃O_x superconductor tapes prepared from fine powders is reported. The tapes were fabricated using the powder-in-tube (PIT) method. The critical temperature, T_c and transport critical current density, J_c were measured at liquid nitrogen temperature by standard four-probe method in conjunction with a CTI cryogenics Model 21 closed cycle refrigerator. A Philips XL-30 scanning electron microscope was used to record the microstructure of the sample. It was found that J_c for these tapes increased by 40% when slow cooled at 1 ºC/min. The 2223 phase generally align almost parallel to the current flow direction. SEM image also shows that larger grains size is visible in high critical current density tapes. We suggested that the decreased in J_c occur when cooled with slower rate than 1 ºC/min is because of the appearance of the 2212 phase by the decomposition of the 2223 phase.