TRANSPORT CRITICAL-CURRENT CHARACTERISTICS OF AG B(P)SCCO TAPES IN MAGNETIC-FIELD/

Silver-sheathed Bi1.7Pb0.4Sr2Ca2Cu3Ox (Ag/B(P)SCCO) tapes have been pr epared by powder-in-tube (PIT) technique in which a process of repeate d rolling and intermediate sintering has been followed. The critical c urrent density (J(c)) has been measured at 4.2 K in magnetic field up to 4.4 T at every stage. An increasing grain alignment and compaction is achieved with decreasing oxide core thickness (t(o)), as revealed b y SEM studies. The inverse dependence of J(c) on t(o) of the tape spec imens can be understood in terms of surface pinning. The J(c) variatio n in the magnetic field (B) is found to obey the B--0.5 type of depend ence at 4.2 K. Consequently, the observed linear relationship between volume pinning force (F-p) and B-0.5 is indicative of flux-pinning con trolled J(c) rather than weak-link controlled. An attempt has been mad e to explain the magnetic field dependence of F-p in terms of Kramer's theory. Using this theory we are able to make a rough estimate of the characteristic scaling field (B) at 4.2 K for various tape specimens .