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

A new high-temperature and nontoxic superconductor Ag_1-xCu_xBa₂Ca_n-1Cu_nO_2n+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-xCu_xBa₂Ca₃Cu₄O_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-xCu_xBa₂Ca₃Cu₄O_11-δ phase is 117.1 K. The relationship between the lattice constant c and the number of CuO₂ layers n is c/2=5.3+3.2n ( Å). The small CuO₂-block spacing (8.5 Å) of this family suggests a lower anisotropy and higher J _c than Hg- and Tl-based superconductor families.