Mono- and multifilamentary Ag-sheathed Tl(1223) tapes

A good control of the Tl content in the Tl(1223) phase was achieved by developing a high pressure synthesis (typically 50 bar He/1 bar O-2) which allows the production of 95% pure ceramics with a critical temperature of about 120 K. Mono- and multifilamentary Ag-sheathed tapes were prepared by the powder-in-tube technique with pre-reacted powder. Transport critical current densities of 15 000 A/cm(2) for short-length (3 cm) and 10 000 A/cm(2) for long length (2 m) were reached for monofilamentary tapes (7 K and 0 T). For multifilamentary tapes the critical current density (6000 A/cm(2)) appears to be independent of the superconducting filament thickness down to about 10 mu m. Studies on the dependence of the transport properties on temperature and magnetic field showed that the transport current is dominated by weak-link phenomenon. The existence of a critical current at very high magnetic fields, however, indicates the presence of well connected (strongly coupled) current paths through the sample. Studies on the distribution of the current showed that the current flows uniformly inside the tapes.