Synthesis of HgBa2CuO4+delta under controlled mercury and oxygen pressures

A three-temperature synthesis technique to obtain pure HgBa2CuO4+delta under controlled mercury and oxygen partial pressures was developed. Mixtures of Co3O4/CoO (or CuO/Cu2O) oxides and HgBa2CuO4+delta/Ba2CuO3+x heated at different temperatures were used to adjust P(O-2) and P(Hg), respectively. At equilibrium conditions for the reaction: HgBa2CuO4+delta double left right arrow Ba2CuO3+x + Hg(g) + (1 + delta - x)/2 O-2, 0.09 < P(O-2) < 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+delta formation as a function of P(Hg), P(O-2) and T was determined as: log P(Hg) + 6040/T + 0.266 log P(O-2) > 5.959. It was also found, that slow cooling down to 600 degrees C under fixed oxygen pressure is required to prepare pure HgBa2CuO4+delta.