TRANSPORT AND MAGNETIZATION 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 att ractive candidates for high field applications are a high transition t emperature (similar to 115 K), and an irreversibility line comparable to YBa2Cu3O7, However, a third important factor is the grain boundary behaviour. We have made detailed transport current-voltage (I-V) and m agnetic studies of a Ag-0.1%Hf sheathed Tl-1223 tape. For low fields ( B < 100 mT) its critical current density J(c) performance displays the ''weak-link'' signatures well-known for polycrystalline YBa2Cu3O7. At high fields however (B > 100 mT) there is a plateau region in its J(c )(B) characteristics. Possible scenarios for inter-granular transport current conduction and dissipation in this region are discussed.