ANNEALING TEMPERATURE-DEPENDENCE OF THE SUPERCONDUCTING PROPERTIES OF AG-SHEATHED BI-PB-SR-CA-CU-O TAPES

In order to improve the critical current density (Jc) and temperature (Tc) of Ag-sheathed Bi-Pb-Sr-Ca-Cu-O tapes, the influences of annealing temperature and cooling rate have been in detail investigated in the process of thermomechanical treatment (TMT) employed here. It was found that the annealing between 1113 and 1118 K followed by cooling with a rate of 0.028 K/s resulted in optimum Jc and Tc. The microstructural investigation made clear that the major superconducting 2223 phase was accompanied by minority 2212 and 2201 phases and several impurity phases of CuO, Ca2PbO4 and (Sr, Ca)3Cu5Ox. As a whole, the lamellae of the 2223 phase align almost parallel to the current flow direction. A degradation of Jc and Tc occured for the condition of 1123 K annealing followed by a cooling with slower rate than 0.014 K/s, because of a remarkable increase of the 2201 phase by the decomposition of the 2223 one. © 1990.