Synthesis of single-phase HgBa2Ca2Cu3O8+δ superconductor

Abstract The third member (Hg-1223) of the recently discovered homologous series HgBa 2 Ca n −1 Cu n O 2 n +2+δ , having a T c of 118 K (as synthesized sample) and 133 K (oxygen-annealed sample), was successfully prepared by the solid state reaction and short-time annealing technique using mixtures of the metal oxides HgO, BaO, CaO and CuO with starting composition HgBa 2 Ca 2 Cu 3 O 8+δ . We found that the combination of very short annealing times with optimum temperatures 715–725°C gives rise to a very effective sintering of the constituents and avoids an excessive loss of Hg. Samples so obtained display a sharp superconducting transition determined both magnetically and resistively. The X-ray diffraction patterns of both the 118 K phase and the 133 K phase indicate a nearly single phase, corresponding to the tetragonal structure of space group P4/mmm and with lattice parameters a= 3.85 A and c= 15.85 A . The resistivity ϱ of such a sample was very low, ∼ 12x10 -3 Ω cm at 300 K, and the ϱ versus T curve was linearly extrapolated to zero resistance at 0 K, being similar to the cases of high-quality high- T c cuprates. Energy dispersive X-ray analysis (EDX) data of several grains of the Hg-1223 sample are in agreement with the proposed chemical formula.