MICROSTRUCTURE AND PHASE EVOLUTION OF ULTRAFINE MGO DOPED BI-2223 AG TAPES/

Ultrafine MgO particles were introduced into Bi2Sr2Ca2Cu3O10/Ag (Bi-22 23/Ag) tapes fabricated by the standard powder-in-tube (PIT) process. It was found that the phase transformation rate is decreased with incr easing MgO concentration, Slight degradation of Bi-2223 formation rate is suggested to be of advantage for grain connectivity and grain alig nment, Excessive doping and high sintering temperature resulted in bad transport properties due to severe agglomeration of MgO particles and the growth of residual secondary phase. The critical current was impr oved from 17 A for undoped sample to nearly 27 A for 1 wt% MgO doped s ample heat-treated at 835 degrees C and/or 839 degrees C. The results of J(c)-B measurements show that the ultrafine MgO particles, as addit ional flux pinning centers, may strengthen flux pinning effectively. ( C) 1997 Elsevier Science B.V.