SUBSTITUTIONS IN HG-CUPRATE SUPERCONDUCTORS

Several substitutions have been attempted in the Hg layer of the Hg 12 12 and 1223 cuprate superconductors. A new series of (Hg, Bi)1212 supe rconducting compounds has been synthesized. The highest T-c of the ser ies (92 K) is found for the composition (Hg0.67Bi0.33)Sr-2 (Y0.5Ca0.5) Cu2O7-delta, With lattice constants a = 3.811 Angstrom and c = 12.002 Angstrom. X-ray diffraction and SEM with EDX analysis confirm that Hg is indeed incorporated in the structure. High-pressure oxygenation at 250 bar and 400 degrees C changes the magnetization curve, adding a se cond transition at similar to 42 K; the 92 K transition remains unchan ged. High-pressure oxygenation of Pb-substituted composition of the 12 23 system, (Hg0.67Pb0.33)Ba2Ca2CU3O8, also leads to the formation of l ow temperature phase with T-c = 67 K. The low T-c phase is associated with the incorporation of extra oxygen, possibly in the Hg layer.