COLD SUBSTITUTION IN MERCURY CUPRATE SUPERCONDUCTORS

By using the high-pressure high-temperature technique, we succeeded in substituting in the mercury cuprate superconductors up to about 40% o f mercury by gold. The samples were studied by X-ray and neutron powde r diffraction, electron microscopy, energy dispersive spectroscopy. AC suceptibility measurements were also performed. The experimental data obtained for the Au substituted Hg-1223 compound indicate that the su bstitution leads to overdoping of the CuO2 layers, with a progressive decrease of cell parameters and T-c with increasing gold content, Taki ng into account these results, we used gold substitution to increase T -c of a Hg-1245 sample up to 110 K. The corresponding unsubstituted sa mples are normally obtained by the high-pressure high-temperature tech nique in an underdoped state with a T-c around 100 K.