NOVEL HOMOLOGOUS SERIES OF SUPERCONDUCTING COPPER OXIDES, CU-12(N-1)N

Perovskite-like structures in a multi-phase Ba-Cu-O sample which was synthesized under high pressure and showed superconductivity at T(c)=117 K have been studied by means of electron diffraction (ED) analysis and high-resolution electron microscopy (HRTEM). Based on the ED analysis, three different phases with perovskite-like structures are identified to possess tetragonal primitive unit cells with lattice parameters a=3.88 angstrom and c=(5.1 + 3.3 n) angstrom where n=3, 4 and 5. The HRTEM observations reveal structures similar to those of members of the Hg-12(n-1)n and/or Tl-12(n-1)n series. Thus, it is most likely that there exists a novel homologous series of superconducting cuprate phases, i.e. Cu-12(n-1)n, whose n=2 member corresponds to the well-known tetragonal ''123'' structure.