New High-T_c Superconductor Ag_1-xCu_xBa₂Ca_n-1Cu_nO_2n+3-δ Family with T_c> 117 K

Abstract

A new high-temperature and nontoxic superconductor Ag 1- x Cu x Ba 2 Ca n -1 Cu n O 2 n +3-δ family with T c >117 K was discovered. These materials are prepared by the high-pressure technique. A superconductor sample with the highest T c contains mainly a Ag 1- x Cu x Ba 2 Ca 3 Cu 4 O 11-δ ( x =0.75) phase. The phase has a body-centered tetragonal structure with lattice constants of a =7.7270 Å and c =36.222 Å. The disordering of Ag sites leads to the space group of P4/mmm and the lattice constants of a =3.8635 Å and c =18.111 Å. The T c value of the Ag 1- x Cu x Ba 2 Ca 3 Cu 4 O 11-δ phase is 117.1 K. The relationship between the lattice constant c and the number of CuO 2 layers n is c /2=5.3+3.2 n ( Å). The small CuO 2 -block spacing (8.5 Å) of this family suggests a lower anisotropy and higher J c than Hg- and Tl-based superconductor families.