TEM investigation of the microstructure and properties of Tl(Bi)-1223/Ag powder-in-tube superconducting tapes

Abstract

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 superconducting tapes using transmission electron microscopy. Melt processing led to a markedly different microstructure compared to that obtained from more conventional primarily solid state reaction routes. Clusters of well connected grains were observed resulting in a denser and more uniform microstructure. This is consistent with an improvement in the magnetic field dependence of the critical current density (Jc) for the melt processed tapes with reduced degradation of Jc in field and an increase in the high-field Jc plateau. In addition, the magnetic screening currents flow on a scale of the same order of magnitude as the grain clusters. The Ag/Tl(Bi)-1223 interface was 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 interface and, as a result, no long-range texture is observed.