Structural and superconducting properties of (Hg_0.7Bi_0.3)Sr₂Ca_n-1Cu_nO_x(n= 3,4) superconductors synthesized under high pressure

Abstract

The third and fourth members (n = 3 and 4) of Hg-Sr, HgSr2Can-1CunOx, series have been stabilized by Bi under high pressure. The phase formation of these phases is found to be sensitive to the nominal oxygen content, x, in the starting mixture. High phase purity is obtained with nominal oxygen contents of 8.55 and 10.15 for n = 3 and 4, respectively. The combined XRD and EDS analyses of the phase with n = 3 show the presence of an excess of strontium 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/H2 atmosphere, respectively. On the other hand, the highest Tc of the sample with nominal composition (Hg0.7Bi0.3)Sr2Ca3Cu4O10.15 was 96 K in the as-prepared form and did not change with annealing.