New ''02(n-1)n'' homologous series consisting of superconducting copper oxyhalide of the Sr-Ca-Cu-O-Cl system

A copper oxyhalide of the Sr-Ca-Cu-O-Cl system has been synthesized using a high-pressure synthesis technique. X-ray and electron-diffraction analyses and high-resolution transmission electron microscopic observation have revealed the formation of a homologous series, 02(n - 1)n, in this system. Depending on the synthesis condition, the sample containing the same phase can be superconducting or non-superconducting. The structural models for the members of this series are proposed. X-ray Rietveld refinement is performed for a nearly single-phase sample of (Sr,Ca)(3)Cu2O4+xCl2-y which shows superconductivity above 80 K. In these samples, it is considered that holes are introduced by the substitution of O2- for Cl- which are located at the apical site of pyramids with CuO2 basal plane.