Structural and Electronic Relationships in the High-Temperature Copper-Based Superconductors

ABSTRACTAtomic displacements from the ideal rock-salt positions in the Tl-, Bi-, and Pb-O layers of the Cu-based high-Tc super-conductors affect the electronic nature of these oxides. When distortions in the Bi-O layers of Bi2Sr2CaCu2O8 are considered, the bottom of the Bi 6p band is found to lie more than 1 eV above the Fermi level. Displacements in the double Tl-O layers of Tl2Ba2Can−1CunO2n+4 places the bottom of the Tl 6s bands significantly below the Fermi level showing that electrons can be removed from the x2-y2 bands of the CuO2 layers. However, this is not the case for the thallium-oxygen single layers of Tl2Ba2Can−1CunO2n+3. Correlations between the superconducting transition temperatures, Tc, and the in-plane Cu-O bond lengths, rCu−O', of the Tl- and Bi- based copper-oxide super-conductors reveal Tc vs rCu−O characteristics similar to those found for La2−xSrxCuO4.