Superconductivity in HgBa2Ca2Cu3O8 + δ synthesized by different methods

The composition and superconducting properties of powder samples of Hg-1223, HgBa2Ca2Cu3O8 + δ, were investigated. The specimens were prepared by a single-step method using individual metal oxides, and by a two-step method in which the precursor Ba2Ca2Cu3O7 ± δ was first synthesized by sol-gel method and then mixed with HgO. The final annealing was performed in sealed quartz ampoules at 665 °C or 860 °C, and the purity of the obtained samples was compared. After oxygen treatment at 300 °C for 6 h the samples showed superconductivity at a Tc (onset) of approximately 134 K, as determined from AC susceptibility measurements. The materials were also studied by X-ray powder diffraction and scanning and transmission electron microscopy.