SINGLE-CRYSTALS OF THE 96 K SUPERCONDUCTOR (HG,CU)BA2CUO4- GROWTH, STRUCTURE AND MAGNETISM(DELTA )

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, Th e as-synthesized crystals exhibit constant T-c(onset) of 96 K with sha rp superconducting transitions. The electron microscopy coupled with E DX analyses evidence a ''1201''-type structure while a mercury deficie ncy is observed balanced by an excess of copper. The structural refine ments based on single-crystal X-ray diffraction data confirm the elect ron deficiency on the Hg site (0,0,0) and show a splitting of the latt er along the c axis correlated to the partial substitution of Cu for H g. This structural study leads to the following formula Hg0.84CU0.16Ba 2CuO4.19. 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 l ine higher than that of the 1201 Hg0.8Bi0.2Ba2CuO4+delta crystal (T-c = 75 K). From the reversible magnetization, a lambda(ab)(O) = 2470 Ang strom value can be extrapolated. Using a 3D-2D decoupling formula, we obtain gamma = 29 for the electronic anisotropy of this phase.