Are One-Dimensional Structural Features Essential for Superconductivity at 90K ?
The crystal structures of the novel high-Tc oxocuprates1,2,3,4 have certain features in common, but also exhibit essential differences. La1.8M0.2CuO4(M=Ba,Sr; Tc ≈ 30 to 40K) contains copper in an average oxidation state +2.2. The coordination octahedron around Cu is tetragonally elongated (d(Cu-O)=190 pm (4x) and 240 pm (2x)). Taking the drastic differences of the Cu-O distances into account, the structure contains CuO2 layers formed from corner-sharing CuO4 squares according to ∞ 2 [CuO4/2] which are sandwiched between rigid slabs of composition ∞ 2 [(La,M)2O2]. Obviously, the layers are only weakly coupled to the surrounding slabs.
KeywordsElectrical Resistivity Oxygen Removal Valence Fluctuation Valence Bond Theory Coordination Octahedron
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