Quadruple and quintuple perovskite-layered cuprates (NdDyBa2-xSrxCu2+yTi2-yO11-delta and NdDyCaBa2-xSrxCu2+yTi3-yO14-delta): Their defect chemistry and electrical properties

The structure-property relationships of chemically substituted quadruple- a nd quintuple-layered cuprate perovskites, NdDyBa2-xSrxCu2+yTi2-yO11-delta a nd NdDyCaBa2-xSrxCu2+yTi3-y O14-delta, have been investigated with an empha sis on high-temperature electrical properties, Cu doping for Ti in both sys tems, especially the quadruple system, improves their electrical properties ; however, substantial compensation by oxygen vacancies occurs. On the othe r hand, isovalent Sr substitution for Ba in these systems significantly red uces the ionic compensation, i,e,, the [V-(O) double over dot ] concentrati on, as evidenced by thermogravimetry and electrical measurements. Sr substi tution 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 degreesC) electrical conductivity and Seebeck coefficient measure ments plus low-temperature resistivity measurements. A master plot of high- temperature Seebeck coefficient vs hole content of known superconductors sh ows that the hole content necessary for superconductivity has been achieved in some of the doped quadruple systems, yet they fail to exhibit supercond uctivity owing to other structural limitations. (C) 2000 Academic Press.