A new high-T_c TlBa₂Ca₃Cu₄O₁₁ superconductor with T_c >120K

Abstract

Three superconducting compounds are known at present in the Tl–Ba–Ca–Cu–O system: Tl₂Ba₂CuO_6+y, Tl₂Ba₂CaCu₂O_8+y, and Tl₂Ba₂Ca₂Cu₃O_10+y, known by their cation numbers as '2201', '2212' and '2223', respectively^1–3. The transition temperature T_c increases in this series, from 80 to 110 to 120 K, as the number of CuO₂ layers in the unit cell increases from one to three. Here we report the synthesis and characterization of a new Tl–Ba-Ca–Cu–O superconductor which differs from these three in having only a single thallium layer (instead of two) per unit cell, but which has four CuO₂ layers. The composition of the phase is TlBa₂Ca₃Cu₄O₁₁ (1234) and its structure is tetragonal, with lattice constants a = 3.85 Å and c = 19.1 Å.