Single crystals of the 96 K superconductor (Hg,Cu)Ba2CuO4+delta: Growth, structure and magnetism

Single crystals of the 1201 (n = 1) (Hg,Cu)Ba2CuO4-delta 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 Hg0.84CU0.16Ba2CuO4.19. The magnetic study of a large crystal (1.1 X 0.38 X 0.065 mm(3)) shows that the (Hg,Cu)-1201 crystals exhibit an irreversibility line higher than that of the 1201 Hg0.8Bi0.2Ba2CuO4+delta crystal (T-c = 75 K). From the reversible magnetization, a lambda(ab)(O) = 2470 Angstrom value can be extrapolated. Using a 3D-2D decoupling formula, we obtain gamma = 29 for the electronic anisotropy of this phase.