100-K superconducting phases in the Tl-Ca-Ba-Cu-O system

Abstract

Two superconducting phases, ${\mathrm{Tl}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{10+\mathrm{\delta }}$ (2223) and ${\mathrm{Tl}}_2$ ${\mathrm{Ca}}_1$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_2$ ${)}_{8+\mathrm{\delta }}$ (2122), both with onset ${\mathrm{T}}_{\mathrm{c}}$ near 120 K and zero resistivity at 100 K, have been isolated from samples in the Tl-Ca-Ba-Cu-O system. The new 2223 superconductor has a 5.40×5.40×36.25-A${\mathrm{̊}}^3$ pseudotetragonal unit cell. The 2122 superconductor, which appears to be structurally related to ${\mathrm{Bi}}_2$ ${\mathrm{CaSr}}_2$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_{8+\mathrm{\delta }}$, has a 5.44×5.44×29.55-A${\mathrm{̊}}^3$ pseudotetragonal subcell. The 2223 phase is probably related to 2122 by the addition of extra calcium and copper layers.