P. Bordet et al., AUBA2(Y1-X,CA-X)CU2O7 - A NEW SUPERCONDUCTING GOLD CUPRATE WITH T-C ABOVE 80 K, Physica. C, Superconductivity, 276(3-4), 1997, pp. 237-244
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 (orthorhombic Pmmm, a = 3.8298(5) Angstrom, b = 3.842
0(5) Angstrom, c = 12.111(1) Angstrom for nominal composition x = 0.4)
is very similar to that of YBa2Cu3O7, with Au3+ cations in square pla
nar coordination sharing corners to form chains running along the b ax
is. Electron microscopy reveals the presence of a superstructure with
double b parameter, which is attributed to a long range ordered zig-za
g conformation of the square chains. For x = 0, the formal copper vale
nce is 2 + and the compound is insulating. Doping of the conducting Cu
O2 planes is achieved by the partial substitution of yttrium by calciu
m, up to x approximate to 0.4. Upon substitution, the compound becomes
superconducting with a maximum T-c at similar to 82 K for x approxima
te to 0.4.