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

• Published in: Physica. C, Superconductivity Superconductivity, 1997-05, Vol.279 (1), p.11-17
• Main Authors: Lokshin, K.A., Kuzemskaya, I.G., Kulikova, L.F., Antipov, E.V., Itskevich, E.S.
• Format: Article
• Language: English
• Subjects: Hg-1223; Hg-1234; High pressure synthesis; Superconductivity in overdoped region
• ISSN: 0921-4534; 1873-2143
• 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 ‘HgBa 2Ca 3Cu 4O x ’, obtained by changing BaO/BaO 2 and Cu 2O/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) A ̊ , c = 15.79(1) A ̊ 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) A ̊ , c = 15.84(1) A ̊ Dependence of T c vs. a-parameter (and consequently, oxygen content δ) for the HgBa 2Ca 2Cu 3O 8+δ superconductor has a cupola-shaped character, as found previously for the lower members of the homologous series.