Formation and Degradation of the 120 K Tc Phase in the Tl-Pb-Sr-Ca-Cu-O System

Abstract

Time-dependent formation and degradation processes of the 120 K T _c phase in the Tl-Pb-Sr-Ca-Cu-O system have been investigated by measuring the temperature-dependent resistivity, and by X-ray diffraction, fluorescent X-ray and EPMA analyses. It is shown that the 80 K T _c phase ((Tl, Pb)(Sr, Ca)₃Cu₂O _x ) changes partly to the 120 K T _c phase ((Tl, Pb)(Sr, Ca)₄Cu₃O _x ) upon prolonged heat treatment, and that the resultant 120 K T _c phase changes again to the 80 K T _c phase upon heat treatment in the presence of an excess amount of Tl₂O₃.