High pressure synthesis and superconducting properties for the multi-layered Ba2Can-1CunO2n(O,F)2 (n = 4 and 5)

We prepared multi-layered oxyfluoride superconductors, Ba2Can-1CunO2n(O,F)(2) (n = 4 and 5) using high-pressure apparatus. These phase are the n = 4 and 5 members of a homologous series, M2Can-1CunO2n(O,F)(2) [0(M)2(n-1)n-F] reported previously. X-ray studies indicated that they have tetragonal structures with a = 3.863 angstrom, c = 33.75 angstrom for n = 4 and a = 3.862 angstrom, c = 40.18 angstrom for n = 5. Superconducting transition temperature were 86.6 K for n = 4 and 75.7 K for n = 5, respectively. The critical current density (J(c)) and irreversibility field (H-irr) were determined from M-H curves using the Bean's model. J(c) and H-irr of 0(Ba)2(n-1)n-F (n = 4 and 5) decreased rapidly with increasing temperature. J(c) (5 K, 1 T) shows 1.70 x 10(6) A/cm(2) for n = 4 and 1.93 x 10(5) A/cm(2) for n = 5. The estimated values of H-irr (5 K) are about 70 T for n = 4 and 17 T for n = 5. (c) 2006 Elsevier B.V. All rights reserved.