Structural and superconducting properties of (Hg0.7Bi0.3)Sr2Can-1CunOx (n=3, 4) superconductors synthesized under high pressure

The third and fourth members (n = 3 and 4) of Hg-Sr, HgSr2Can-1CunOx, serie s have been stabilized by Pi under high pressure. The phase formation of th ese phases is found to be sensitive to the nominal oxygen content, x, in th e starting mixture. High phase purity is obtained with nominal oxygen conte nts of 8.55 and 10.15 for n = 3 and 4, respectively. The combined XRD and E DS analyses of the phase with n = 3 show the presence of an excess of stron tium in the calcium sites. The sample with nominal composition (Hg0.7Bi0.3) Sr2Ca2Cu3O8.55 was overdoped and exhibited bulk superconductivity below 105 and 116 K in the as-prepared form and after annealing in Ar/H-2 atmosphere , respectively. On the other hand, the highest T-c of the sample with nomin al composition (Hg0.7Bi0.3)Sr2Ca3Cu4O10.15 was 96 K in the as-prepared form and did not change with annealing.