Dependence of Tc on the Hole Concentration in Superconducting Thallium Cuprates with Single Tl-O Layers

Band structure calculations have indicated that in the double-Tl–O-layer cuprates, the bottom of the Tl(6s) band lies significantly below the Fermi level, while in the single-Tl–O-layer cuprates the Tl(6s) band lies well above the Fermi level. The metal chemistry of the single-Tl–O-layer cuprates is such as to create holes in the CuO2 layers. In the two-Tl–O-layer cuprates, it has been suggested that an internal oxidation-reduction reaction mechanism could be operative. Superconducting transition temperatures (Tc) of the cuprate superconductors have been correlated with a large number of structural parameters, such as in-plane Cu–O bond lengths, bond valence sums, Madelung potentials, and the electronegativity of the constituent ions. Among these, the in-plane Cu–O bond length is an important structural parameter that reflects the extent of oxidation of the CuO2 layer on doping.