2 NEW HG-SR CUPRATE SUPERCONDUCTORS

Two new series of Hg-Sr cuprate superconductors: (a) (Hg,Mo)Sr2CuO4+de lta and (b) (Hg,Bi)Sr-2(Ca,Y)Cu2O7-delta have been synthesized. Hg-Sr superconductors, which are otherwise difficult to make, have been stab ilized by partial substitution of higher-valent cations for Hg. T-c ho wever, is substantially reduced as compared to the corresponding unsub stituted Hg-Ba cuprate superconductor. The best T-c in series (a) is 7 8 K for (Hg0.85Mo0.15)Sr2CuO4+delta and that in series (b) is 92 K for (Hg0.67Bi0.33)Sr-2(Y0.5Ca0.5)Cu2O7-delta as compared to 95 K and 125 K respectively for the corresponding unsubstituted Hg-Ba cuprates. In both series, high p(O2) annealing lowers the T-c even further suggesti ng that the samples are overdoped and the substitution of higher-valen t cation for Hg did not decrease the hole concentration. Addition of M o/Bi appears to be accompanied by the uptake of additional oxygen, del ta, which go to the Hg-O delta layer and the lowering of T-c results f rom the presence of these extra oxygens in the Hg layer.