SINGLE-STEP SYNTHESIS OF BULK HGBA2CA2CU3O8+DELTA

Bulk superconducting samples of nearly phase-pure HgBa2Ca2Cu3O8+delta (hereafter denoted as Hg- 1 22 3) were prepared by a solid-state reaction of stoichiometric quantities of HgO, BaO, CaO and CuO in a single step. The starting mixtures were ground, pressed into a pellet, sealed in a quartz tube, and heated to 840-860-degrees-C. The ''as-synthesized'' Hg-1223 samples had a T(c) of 110-112 K, as defined by the onset of diamagnetism. The crystal symmetry was found to be tetragonal with a space group of P4/mmm, and lattice parameters a = 3.852(1) angstrom and c = 15.830 (1) angstrom, similar to the values for TlBa2Ca2Cu3O9-delta. Finely ground powders were stable upon exposure to ambient air for a period of approximately 4 days. On annealing in 1 atm oxygen at 300-degrees-C for 6 h, these samples gained weight (corresponding to approximately 0.066-0.075 oxygen atoms per formula unit) and displayed sharp superconducting transitions up to 134.5 K. Using this procedure, high-quality Hg-1223 samples can be easily synthesized.