Tl-based superconductors for high-current, high-field applications

We have reviewed the convenience and possibility of utilizing thallium-based superconductors for power applications. Some basic properties of Tl-based systems such as the crystal structure, phase stability, weak-links, pinning problems and irreversibility lines are discussed first. Two basic approaches to conductor preparation are then described, the closed and the open one. Special attention is focused on the fabrication of Tl-1223 and Tl-2223 superconductors. In the case of the more successful open approach a two-step technological procedure is usually chosen: first, the basic precursor material without Tl is synthesized, then second, the precursor is thallinated in a one- or two-zone reaction chamber. The most important precursor preparation techniques are described including aerosol deposition from either solution or ink, electro-deposition, sol-gel methods such as spin- and dip-coating and screen-printing and painting. Finally, some properties of the produced conductors important for power applications are presented.