SUPERCONDUCTIVITY UP TO 32-K IN A NEW FAMILY OF THE HG-CONTAINING (PB,HG) (SR,LA)2CUO5-DELTA (1201) SYSTEM

A new family of superconductors with a maximum T(c) of 32 K were observed in the Hg-containing (Pb0.5Hg0.5) (Sr2-xLax)CuO5-delta (I 20 1 ) system for the composition range 0.8 less-than-or-equal-to x less-than-or-equal-to 1.0. The chemical composition and crystal structure of this system have been investigated by X-ray powder diffraction including the Rietveld refinement, electron diffraction, and high-resolution transmission electron microscopy. We have identified the phase responsible for the superconductivity to be similar to (Pb, Cu) (Sr, La)2CuO5, or (Tl, Pb) (Sr, La)2CuO5 (the so-called 1201 phase) with a space group of P4/mmm and lattice constants of a = 3.7908 (2) angstrom and c = 8.6915 (6) angstrom for the x = 0.8 sample in (Pb0.5Hg0.5) (Sr2-xLax) CuO5-delta. The disordering of the hole reservoir layer of (Pb, Hg)O due to the displacement of the oxygen ion from its ideal position (0.5, 0.5, 0) to (0.33, 0.5, 0) was found by Rietveld refinement for powder X-my diffraction data of the x = 0.8 sample. This displacement may give rise to the appearance of the superlattice spots along the [102]* direction with a modulation factor close to 4 in the electron diffraction pattern viewed down [010].