High pressure synthesis of Hg-1234 and strongly-overdoped Hg-1223 phases

Article abstract of DOI:10.1016/S0921-4534(97)00084-1

The Hg-1223 and Hg-1234 phases were synthesized using the program-controlled high pressure chamber. The variation of the oxygen content in the starting oxides mixture `HgBa₂Ca₃Cu₄O_x', obtained by changing BaO/BaO₂ and Cu₂O/CuO ratios, influences significantly the phase formation. By varying the pressure (P_s), temperature (T_s), time (t_s) and oxygen content (x), the optimum synthesis conditions of the Hg-1234 phase were determined with P_s = 2 GPa, T_s = 900 °C, t_s = 2 h and x = 10.2. Using the initial mixture with the high oxygen content (x = 10.6) only Hg-1223 with the lattice constants a = 3.8474(9) angstroms, c = 15.79(1) angstroms was obtained. Hg-1223 thus prepared is strongly overdoped and exhibits superconductivity at 118 K, while the treatment in oxygen flow enhanced T_c up to 134 K and cell parameters to a = 3.852(1) angstroms, c = 15.84(1) angstroms. Dependence of T_c vs. a-parameter (and consequently, oxygen content δ) for the HgBa₂Ca₂Cu₃O_8+δ superconductor has a cupola-shaped character, as found previously for the lower members of the homologous series.