New High-T_c Superconductor Family of Cu-Based Cu_1-xBa₂Ca_n-1Cu_nO_2n+4-δ with T_c>116 K

Abstract

A new high-temperature and nontoxic superconductor family of Cu 1-x Ba 2 Ca n-1 Cu n O 2 n +4-δ with critical temperature ( T c )>116 K was discovered. These materials were prepared by the high-pressure technique. A superconductor sample with the highest T c contains mainly a Cu 1- x Ba 2 Ca 3 Cu 4 O 12-δ phase. The T c value of the Cu 1- x Ba 2 Ca 3 Cu 4 O 12-δ phase is 116.4 K. The phase has two kinds of tetragonal structures: body-centered tetragonal (bct) and simple tetragonal. The lattice parameters of bct are a =7.7114 Å and c =35.986 Å. The disordering or full occupation of Cu-vacancy sites leads to the simple tetragonal phase with the space group of P4/mmm and the half values of the lattice constants ( a =3.8557 Å and c =17.993 Å) of the bct phase. The relationship between the lattice constant c and the number of CuO 2 layers n is c /2=8.4+3.2( n -1) ( Å). The small CuO 2 -block spacing (8.4 Å) of this family suggests a lower anisotropy and higher J c than in Hg- and Tl-based superconductor families.