Crystal chemistry and superconductivity of the copper oxides

Description/Abstract

This paper highlights the important roles played by crystal chemistry in controlling the superconductive properties of the intergrowth structures of the copper oxides. Bond-length matching across the intergrowth interface stabilizes at least four different structures - T/O, T{prime}, T*, and T{double prime} - in the simplest system La{sub 2{minus}y}Ln{sub y}CuO{sub 4} (Ln = lanthanide) depending upon the size of Ln and the value of y. The internal electric field created by the formal charges in the adjacent layers modulates the distribution of holes between the active and inactive layers and the influence of Pr on superconductivity. The coordination geometry preferred by different oxidation states of Cu appears to control the oxygen ordering and the T{sub c} variation in the YBa{sub 2}Cu{sub 3}O{sub 6+x} system. The c-axis Cu-O distance modulates the width of the conduction band and the electronic properties.