SYNTHESIS, STRUCTURE, AND PROPERTIES OF THE HIGH-TEMPERATURE SUPERCONDUCTOR HGBA2CUO4+DELTA

We report here the attempted synthesis of (Hg1-xCuy)Ba2CuO4+delta (0 l ess than or equal to x less than or equal to 0.2, 0 less than or equal to y less than or equal to 0.2, y less than or equal to x) and the re sults of a detailed characterization of the structural and superconduc ting properties of the resulting samples. Rietveld refinement of powde r x-ray-diffraction data collected on all 15 samples synthesized found no partial Cu occupancy of the Hg site. We therefore conclude that fo r these samples no solid solution exists and the superconducting phase is simply HgBa2CuO4+delta. Only one interstitial oxygen position O(3) was found, located exactly at the center of the Hg plane. An analysis of the structural refinements has produced a number of correlations b etween the exact location of the Ba2+ cation within the unit cell and a number of important superconducting parameters; these include the oc cupancy of the O(3) site, the extent of oxidation of the CuO2 planes, and the magnetic penetration depth.