Transport and magnetisation measurements of Tl-1223 tapes-the nature of current paths and the role of grain boundaries at high magnetic fields

The key factors that make the thallium-based 1223 phase conductors attractive candidates for high field applications are a high transition temperature (/spl sim/ 115 K), and an irreversibility line comparable to YBa/sub 2/Cu/sub 3/O/sub 7/. However, a third important factor is the grain boundary behaviour. We have made detailed transport current-voltage (I-V) and magnetic studies of a Ag-0.1%Hf sheathed Tl-1223 tape. For low fields (B<100 mT) its critical current density J/sub c/ performance displays the "weak-link" signatures well-known for polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7/. At high fields however (B>100 mT) there is a plateau region in its J/sub c/(B) characteristics. Possible scenarios for inter-granular transport current conduction and dissipation in this region are discussed.