Formation behavior of high-Tc Tl-based superconductors

The effects of Ca, Cu, and Ca-Cu richness on the formation behavior and physical characteristics of high-T-c Tl-based superconductors were investigated systematically. In addition to sintering temperature and time, intermediate phases which proved important to the formation and properties of nearly single-phase, triple-CuO-layers Tl2Ba2Ca2Cu3Oy superconductors and optimal processing conditions were also investigated. Ca and Ca-Cu richness introduced positive effects on the properties of nearly single-phase Tl2Ba2Ca2Cu3Oy superconductors and helps in the formation of the appropriate intermediate phases, whereas Cu richness produced a negative effect. The higher sintering temperatures of the specimens accounted for the tailing of electrical resistance before the critical zero resistance temperature was approached, and for the instability of the superconducting phase. Lower post-annealing temperatures of the bulk samples slightly improved the superconducting properties. The resultant bulk Tl-based superconductors can be used as a Tl vapor source for the formation of superconducting thin films within a closed system.