THE HIGH-PRESSURE AND HIGH-TEMPERATURE SYNTHESIS OF HGBA2CACU2O6+DELTA AND HGBA2CA2CU3O(8+DELTA) SUPERCONDUCTORS AND THEIR CHARACTERIZATION

The superconductors HgBa2CaCu2O6+delta (Hg-1212) and HgBa2Ca2Cu3O8+del ta (Hg-1223) have been synthesized by solid state reaction, carried ou t at 850 degrees C under 25 kbar, using the nominal composition of HgB a2Ca2Cu3Ox. The results indicate that the optimum sintering time for t he Hg-1223 phase is about 0.5 h. With increasing sintering time, the H g-1223 phase decomposes, and the Hg-1212 phase increases gradually. Wh en the sintering time increased to 3.8 h, we obtained a sample with ne arly a single phase of Hg-1212. We synthesized the HgBa2CaCu2O6+delta superconductor under 27 kbar at various sintering temperatures using t he 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 O-2 on the superconductivity of HgBa2Ca2Cu3O8+delta has been investigated.