Crystallography and microstructure of Tl-Ca-Ba-Cu-O superconducting oxides

We report on the crystallography and microstructure of six oxides in the Tl-Ca-Ba-Cu-O system with nominal compositions Tl1Ba 2Cu1O5, Tl1Ca1Ba 2Cu2O7, Tl1Ca2Ba 2Cu3O9, Tl2Ba2Cu 1O6, Tl2Ca1Ba2Cu 2O8, and Tl2Ca2Ba2Cu 3O10. The structures consist of one, two, or three Cu perovskite-like units sandwiched between Tl-O monolayers or bilayers. The predominant defects in the crystals with bilayer and trilayer Cu perovskite-like units are stacking faults that produce local intergrowths of related structures. The density of stacking defects in these oxides correlates with changes in the superconducting transition temperatures.