Au-1212: A new superconducting gold cuprate with Tc above 80 K

Abstract

We have synthesised by the high pressure-high temperature technique a new layered gold cuprate of chemical formula AuBa 2(Y 1−x,Ca x)Cu 2O 7 (0≤x≤0.4) (hereafter denoted as Au- 1212). The structural properties of this compound are investigated by means of electron microscopy and powder x-ray diffraction. The average structure (Pmmm, a≈3.83Å,b≈3.84Åc≈12.11Å) is similar to that of YBa 2Cu 3O 7, with square-coordinated Au 3+ cations forming chains along b by corner sharing. Electron microscopy reveals the presence of a superstructure with double b parameter, which is attributed to a long range ordered zig-zag conformation of the chains. For x=0, the formal copper valence is 2+ and the compound is insulating. Doping of the conducting CuO 2 planes is achieved by the partial substitution of yttrium by calcium, up to x≈0.4. Upon substitution, the compound becomes superconducting with a maximum Tc at ≈82K for x≈0.4.