SYNTHESIS AND MAGNETIC CHARACTERIZATION OF THE HIGH-T(C) SUPERCONDUCTING COMPOUND HGBA2CUO4+DELTA

Bulk superconducting samples of HgBa2CuO4+delta (hereafter denoted as Hg-1201) were prepared by solid state reaction of stoichiometric quant ities of HgO and Ba2CuO3 precursors. The ''as-synthesized'' Hg-1201 sa mples had a T(c) of 95 K, as defined by the onset of diamagnetism. The crystal symmetry was found to be tetragonal with lattice parameters, a = 3.876(2) angstrom, and c = 9.515 (3) angstrom, similar to the lite rature values. Finely ground X-ray specimens were stable upon exposure to ambient air for a period of approximately 24 h. Magnetic character izations were conducted using a SQUID based DC magnetometer. Studies o f the transition region in low applied fields showed complete screenin g and evidence for weak intergrain coupling of the randomly oriented c rystallites. High field magnetic hysteresis studies showed rapid decay of hysteresis of the magnetization (proportional to the current densi ty), both with applied field and temperature, These findings are attri buted to the presence of substantial thermally activated flux motion.