Effects of Inherent (Auto) Doping and Oxygen Nonstoichiometry and Their Relationship to the Band Structure of Tl-Based Superconductors

Although both the single- and double-thallium-layer series possess similarities in both composition and structure, there are, nevertheless, remarkable differences in their chemical and physical properties. Oxygen nonstoichiometry is known to play a pivotal role in the geometric and electronic structure of high-T_c superconducting cuprates. In granular high-T_cs cuprate superconductors, it is a common observation that the transport critical current density in a well-sintered bulk sample is very much smaller than the corresponding value deduced from magnetic hysteresis measurements. It was found that the superconductivity in these materials was dramatically modified by oxygen nonstoichiometry. Thus, the authors have demonstrated that oxygen nonstoichiometry is highly dependent on the precise nature and location of cations in the rock salt–type sheets in single-thallium-layer cuprate systems.