Well-defined grain boundary weak-links in silver-sheathed ( tape conductors

The key factors that make the thallium-based 1223 phase conductors attractive candidates for high-field applications at 77 K are a high transition temperature (about 115 K) and an irreversibility line comparable to that of . However, a third important factor is the grain boundary behaviour. We have performed detailed current - voltage (I - V) studies of a silver-sheathed ( (Tl-1223/Ag) tape. Although the tape has a fairly high self-field critical current density at 77 K (about ), the I - V characteristics display the `weak-link' signatures well known for : linear dissipation above a sharply defined critical current, a pronounced decrease of in a magnetic field H and hysteresis with respect to field cycling. Broader implications for the superconductive behaviour of HTS grain boundaries are discussed.