Quadruple and Quintuple Perovskite-Layered Cuprates (NdDyBa2−xSrxCu2+yTi2−yO11−δ and NdDyCaBa2−xSrxCu2+yTi3−yO14−δ): Their Defect Chemistry and Electrical Properties

Abstract

The structure–property relationships of chemically substituted quadruple- and quintuple-layered cuprate perovskites, NdDyBa2−xSrxCu2+yTi2−yO11−δ and NdDyCaBa2−xSrxCu2+yTi3−yO14−δ, have been investigated with an emphasis on high-temperature electrical properties. Cu doping for Ti in both systems, especially the quadruple system, improves their electrical properties; however, substantial compensation by oxygen vacancies occurs. On the other hand, isovalent Sr substitution for Ba in these systems significantly reduces the ionic compensation, i.e., the [V··O] concentration, as evidenced by thermogravimetry and electrical measurements. Sr substitution not only reduces the Cu–O bond length in favor of hole formation but also introduces metallic behavior as evidenced by in situ high-temperature (800–400°C) electrical conductivity and Seebeck coefficient measurements plus low-temperature resistivity measurements. A master plot of high-temperature Seebeck coefficient vs hole content of known superconductors shows that the hole content necessary for superconductivity has been achieved in some of the doped quadruple systems, yet they fail to exhibit superconductivity owing to other structural limitations.