High Pressure Synthesis of HgBa2(Sr,Ca)2Cu3O8 Superconductor

With the aim of improving superconducting properties of HgBa2Ca2Cu3O8’ partial substitution of Sr for Ca was attempted. A high pressure technique was utilized for the synthesis. HgO, BaO2, SrO2, CaO, CuO and Cu metal powders were mixed at a nominal composition of HgBa2(Ca1-xSrx)2Cu3Oy, (x = 0.0 and 0.3, y = 7.8 — 8.2) and heat-treated at 800 — 1100 0C for 1 — 4 h at 5 — 6 GPa. Nearly single-phase samples with x = 0.0 and 0.3 could be prepared. The lattice parameters for the samples werea = 3.857 A and c = 15.85 A for x = 0.0 and a = 3.865 A and c = 15.826 A for x = 0.3, respectively. Compositional analysis using an X-ray microanalyzer indicated that Sr goes to both the Ba and Ca sites. These samples exhibited Tc ’S of 133 K and 128 K, respectively. The irreversibility field, Birr, for the Sr-substituted sample was slightly lowered as compared with that of the pristine one. However, both the samples exhibited higher Birr’S than the reported value for HgBa2Ca2CuO8 prepared at ambient pressure.