AU-1212 - A NEW SUPERCONDUCTING GOLD CUPRATE WITH TC ABOVE 80 K

We have synthesised by the high pressure-high temperature technique a new layered gold cuprate of chemical formula AuBa2(Y1-x,Ca-x)Cu2O7 (0 less than or equal to x less than or equal to 0.4) (hereafter denoted as Au-1212). The structural properties of this compound are investigat ed by means of electron microscopy and powder x-ray diffraction. The a verage structure (Pmmm, a approximate to 3.83 Angstrom, b approximate to 3.84 Angstrom, c approximate to 12.11 Angstrom) is similar to that of YBa2Cu3O7, with square-coordinated Au3+ cations forming chains alon g b by corner sharing. Electron microscopy reveals the presence of a s uperstructure with double b parameter, which is attributed to a long r ange ordered zig-zag conformation of the chains. For x = 0, the formal copper valence is 2+ and the compound is insulating. Doping of the co nducting CuO2 planes is achieved by the partial substitution of yttriu m by calcium, up to x approximate to 0.4. Upon substitution, the compo und becomes superconducting with a maximum Tc at approximate to 82K fo r x approximate to 0.4.