Superconducting Phases with Tc above 100 K in the Tl-Ba-Ca-Cu-O System

Abstract

Superconductivity above 100 K was observed in Tl-Ba-Ca-Cu oxides. DC resistivity, ac susceptibility, EPMA and X-ray diffraction studies revealed that two superconducting phases with different T _c's of ∼110 K and 100 K exist in this oxide system. The 110 K phase is Tl₂Ba₂Ca₂Cu₃O _x (2223 phase) with a 5.45×5.45×35.6 Å tetragonal unit cell, while the 100 K phase is Tl₂Ba₂Ca₁Cu₂O _x (2212 phase) with a 5.45×5.45×29.3 Å tetragonal unit cell. The crystal structure of the 2212 phase seems quite similar to that of Bi₂Sr₂Ca₁Cu₂O _x , and the 2223 phase structure can be derived by inserting another Cu and Ca layer into the 2212 phase.