NEW MERCURY-BASED SUPERCONDUCTORS WITH THE 1201 STRUCTURE HG0.4PR0.6SR2-XPRXCUO4+DELTA AND HG0.3PB0.7SR2-XLAXCUO4+DELTA

To families of mercury-based superconductors, Hg0.4Pr0.6Sr2.xCuO+delta and Hg0.3Pb0.7Sr2-xLaxCuO4+delta, with a T(conset) of 41 K, have been isolated. The Praseodymium phase exhibits a narrow existence range with x less-than-or-equal-to 0.1; in the lead phase, lanthanum can be substituted for strontium up to x = 0.65. The X-ray diffraction and high-resolution electron microscopy analyses show that they both belong to the ''1201'' series; the structures can be described from the intergrowth of single perovskite layers with double oxygen-deficient rock-salt layers built up from the mixed layers [Hg0.4Pr0.6Odelta]infinity and [Hg0.3Pb0.7Odelta]infinity. Evidence is found for ordering between mercury and praseodymium and a structural model is proposed.