We systematically synthesized (Hg,W)-1222 cuprates, (Hg,M)Sr2(Ln,Ce)2Cu2Oz under 2 GPa at 1100°C. Single of nearly single-phase compounds are successfully obtained fix M = Ti, V, Cr, Mo, W and Re, and for Ln = Sm-Er. The structure of these compounds belongs to the same family of 1222 phase and is derived from that of (Hg,M)OSr2(Ca,Ln)Cu2Oz by replacing the single (Ca,Ln) layer with a double fluorite (Ln,Ce)2O2 layer. The (Hg0.75W0.25)Sr2(Gd1.5Ce 0.5)Cu2Oz compound crystallizes in a tetragonal lattice with cell parameters a = 3.832, c = 29.150 Å. All synthesized samples, except for the compound with Cr, show bulk superconductivity with large Meissner volume fractions. Tc was found to increase with increasing valence of the cation M and with decreasing ionic radius of Ln. The maximum Tc of 75 K is obtained for (Hg0.75W0.25)Sr2(Gd1.5Ce 0.5)Cu2Oz.
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