The high-pressure and high-temperature synthesis of HgBa2CaCu2O6+δ and HgBa2Ca2Cu3O8+δ superconductors and their characterization

The superconductors HgBa2CaCu2O6+δ (Hg-1212) and HgBa2Ca2Cu3O8+δ (Hg-1223) have been synthesized by solid state reaction, carried out at 850 degrees C under 25 kbar, using the nominal composition of HgBa2Ca2Cu3Ox. The results indicate that the optimum sintering time for the Hg-1223 phase is about 0.5 h. With increasing sintering time, the Hg-1223 phase decomposes, and the Hg-1212 phase increases gradually. When the sintering time increased to 3.8 h, we obtained a sample with nearly a single phase of Hg-1212. We synthesized the HgBa2CaCu2O6+δ superconductor under 27 kbar at various sintering temperatures using the nominal composition of HgBa2CaCu2Ox. The results indicate that the optimum sintering temperature for the Hg-1212 phase is 820-830 degrees C. The effect of annealing at various temperatures in flowing O2 on the superconductivity of HgBa2Ca2Cu3O8+δ has been investigated. (author)