PEROVSKITE STACKING IN THE STRUCTURES OF THE HIGH-TEMPERATURE CUPRATESUPERCONDUCTORS

Most of the known cuprate superconductors belong structurally to one f amily and are closely related to each other. Ignoring odd structural d etails and considering the idealized structures only, most of them ado pt a Ruddlesden-Popper (R-P) or an oxygen-deficient R-P structure with or without intergrowth layers which are composed of either a rock-sal t type atomic arrangement, chains, bare cations, or a mixture of them. The rock-salt layers found in R-P structures are simply the result of the stacking of perovskite unit cells. Sometimes a fluorite type stru ctural unit can be found, but the structures containing fluorite block s may also be considered to be of the R-P structure type with minor re adjustment of anions in the rock-salt layers to stabilize the structur e. A general formula can be used to describe the basic structures of a ll the cuprate superconductors, even those having fluorite units.