Synthesis of HgBa₂Ca₃Cu₄O_y under ambient pressure

The mercury-based oxide superconductor, HgBa₂Ca₃Cu₄O_y phases was synthesized by a controlled vapor/solid reaction technique using high-purity powders of HgO, BaO, CaO and CuO as starting materials. Two types of bars, with different cation ratios of Hg:Ba:Ca:Cu=0:2:2:3 and 1:2:2:3, were heated in an evacuated quartz tube. The resulting HgBa₂Ca₃Cu₄O_y sample had a T_c of 123 K and lattice parameters a=3.852(2) Å and c=19.01(4) Å with a volume fraction of 83% of the total shielding signal. The formation condition was widely investigated, showing that the higher heating temperature and longer heating time lead to the formation of the HgBa₂Ca_nCu_n-1O_y phase with a higher number n of Cu-O₂ planes in a unit cell.