AuBa 2(Y 1− x, Ca x)Cu 2O 7: 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 ≤ × ≤ 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 (orthorhombic Pmmm, a = 3.8298(5) A ̊ , b = 3.8420(5) A ̊ , c = 12.111(1) A ̊ for nominal composition x = 0.4) is very similar to that of YBa 2Cu 3O 7, with Au 3+ cations in square planar coordination sharing corners to form chains running along the b axis. 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 square 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 T c at ∼ 82 K for x ≈ 0.4.