TEM INVESTIGATION OF THE MICROSTRUCTURE AND PROPERTIES OF TL(BI)-1223AG POWDER-IN-TUBE SUPERCONDUCTING TAPES/

We have made a detailed study of the microstructure of (Tl0.78Bi0.22) (Sr1.6Ba0.4)Ca2Cu3Ox/Ag (Tl(Bi)-1223/Ag) powder-in-tube superconductin g tapes using transmission electron microscopy. Melt processing led to a markedly different microstructure compared to that obtained from mo re conventional primarily solid state reaction routes. Clusters of wel l connected grains were observed resulting in a denser and more unifor m microstructure. This is consistent with an improvement in the magnet ic field dependence of the critical current density (J(c)) for the mel t processed tapes with reduced degradation of J(c) in field and an inc rease in the high-field J(c) plateau. In addition, the magnetic screen ing currents flow on a scale of the same order of magnitude as the gra in clusters. The Ag/Tl(Bi)-1223 interface wits also studied and Tl(Bi) -1223 was shown to align preferentially on a flat Ag surface with the (001)(Tl-1223) planes parallel to the interface. The morphology of the Ag surface is often too rough to maintain the alignment along the int erface and as a result, no long-range texture is observed.