THE SYNTHESIS AND CHARACTERIZATION OF THE HGBA2CA2CU3O8+DELTA-PHASE AND HGBA2CA3CU4O10+DELTA-PHASE

The third (Hg-1223) and the fourth (Hg-1234) members of the recently-discovered homologous series HgBa2Can-1CunO2n+2+delta have been synthesized by solid state reaction, carried out at 950-degrees-C under 50 kbar at different annealing times. These phases have a tetragonal cell with lattice parameters: a=3.8532(6) angstrom, c=15.818(2) angstrom and a=3.8540(3) angstrom, c=19.006(3) angstrom, respectively.The c parameters are in agreement with the formula c congruent-to 9.5 + 3.2(n-1). Electron microscopy study showed similar lattice parameters as well as the occurrence of different intergrowths and stacking faults. A periodicity of 22 angstrom has also been detected, which may be attributed to the existence of the Hg-1245 phase. EDS analysis data of several grains of Hg-1223 and Hg-1234 are in agreement with the proposed chemical formulae. AC susceptibility measurements show that an increase of the superconducting transition temperature with n in the HgBa2Can-1CunO2n+2+delta series occurs till the third member, after which a saturation seems to be achieved.