Abstract
We systematically synthesized (Hg,M)-1222 cuprates, (Hg,M)Sr-2(Ln,Ce)(2)Cu2Oz under 2 GPa at 1100 degreesC. Single or nearly single-phase compounds are successfully obtained for M = Ti, V, Cr, Mo, W and Re, and far Ln = Sm-Er. The structure of these compounds belongs to the same family of 1222 phase and is derived from that of (Hg,M)Sr-2(Ca,Ln)Cu2Oz by replacing the single (Ca,Ln) layer with a double fluorite (Ln,Ce)(2)O-2 layer. The (Hg0.75W0.25)Sr-2(Gd1.5Ce0.5)Cu2Oz compound crystallizes in a tetragonal lattice with cell parameters a = 3.832, c = 29.150 W. All synthesized samples, except fix the compound with Cr, show bulk superconductivity with large Meissner volume fractions. T-c was found to increase with increasing valence of the cation M and with decreasing ionic radius of Ln. The maximum T-c of 75 K is obtained for (Hg0.75W0.25)Sr-2(Gd1.5Ce0.5)Cu2Oz.