A three-temperature synthesis technique to obtain pure HgBa2CuO4+δ under controlled mercury and oxygen partial pressures was developed. Mixtures of Co3O4/CoO (or CuO/Cu2O) oxides and HgBa2CuO4+δ/Ba2CuO3+x heated at different temperatures were used to adjust P(O2) and P(Hg), respectively. At equilibrium conditions for the reaction: HgBa2CuO4+δ ⇔ Ba2CuO3+x + Hg(g) + (1 + δ - x)/2 O2, 0.09 < P(O2) < 0.62 bar and 1009 < T < 1153 K, the mercury partial pressure was found to vary from 1.7 to 6.5 bar. With these conditions, the lower boundary of HgBa2CuO4+δ formation as a function of P(Hg), P(O2) and T was determined as: log P(Hg) + 6040/T + 0.266 log P(O2) > 5.959. It was also found, that slow cooling down to 600°C under fixed oxygen pressure is required to prepare pure HgBa2CuO4+δ.
- HgBaCuO4 + δ
- Mercury partial pressure
- Solid state-gaseous phase equilibrium