Formation behavior of high-T-c Tl-based superconductors

The effects of Ca, Cu, and Ca-Cu richness on the formation behavior and phy sical characteristics of high-T-c Tl-based superconductors were investigate d systematically. In addition to sintering temperature and time, intermedia te 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 introdu ced positive effects on the properties of nearly single-phase Tl2Ba2Ca2Cu3O y superconductors and helps in the formation of the appropriate intermediat e phases, whereas Cu richness produced a negative effect. The higher sinter ing temperatures of the specimens accounted for the tailing of electrical r esistance before the critical zero resistance temperature was approached, a nd for the instability of the superconducting phase. Lower post-annealing t emperatures of the bulk samples slightly improved the superconducting prope rties. The resultant bulk Tl-based superconductors can be used as a Tl vapo r source for the formation of superconducting thin films within a closed sy stem.