New series of oxide superconductors, BSr2Can-1CunO2n+3 (n = 3 approx. 5), prepared at high pressure

Article abstract of DOI:10.1016/0921-4534(95)00566-8

Recently, a new oxyborate superconductor with T_c = 110 K, BSr₂Ca₃Cu₄O₁₁, was prepared under high pressure [E. Takayama-Muromachi et al., Physica C 241 (1995) 137]. This phase is thought to be the n = 4 member of a homologous series, BSr₂Ca_n-1Cu_nO_2n+3. In this paper, we report new members of the series, BSr₂Ca₂Cu₃O₉ (n = 3) and BSr₂Ca₄Cu₅O₁₃ (n = 5), which were prepared under 6 GPa. These members showed T_c's of 75 K and 85 K, respectively. Their X-ray powder diffraction patterns could be indexed assuming tetragonal cells with a = 3.821(1), c = 13.854(6) angstrom for n = 3 and a = 3.837(2), c = 20.22(1) angstrom for n = 5. HRTEM observations indicated that they are essentially isomorphous with Tl(or Hg)-1223 and 1245.