Single crystals of the 96 K superconductor (Hg,Cu)Ba 2CuO 4+δ: growth, structure and magnetism

Abstract

Single crystals of the 1201 ( n = 1) (Hg,Cu)Ba 2CuO 4+δ mercury based cuprate have been grown by using a simple process without dry box. The as-synthesized crystals exhibit constant T c(onset) of 96 K with sharp superconducting transitions. The electron microscopy coupled with EDX analyses evidence a “1201”-type structure while a mercury deficiency is observed balanced by an excess of copper. The structural refinements based on single-crystal X-ray diffraction data confirm the electron deficiency on the Hg site (0,0,0) and show a splitting of the latter along the c axis correlated to the partial substitution of Cu for Hg. This structural study leads to the following formula Hg 0.84Cu 0.16Ba 2CuO 4.19. The magnetic study of a large crystal (1.1 × 0.38 × 0.065 m 3) shows that the (Hg,Cu)-1201 crystals exhibit an irreversibility line higher than that of the 1201 Hg 0.8Bi 0.2Ba 2CuO 4+δ crystal ( T c = 75 K). From the reversible magnetization, a λ ab (0) = 2470 A ̊ value can be extrapolated. Using a 3D-2D decoupling formula, we obtain γ = 29 for the electronic anisotropy of this phase.