Phase coexistence and critical temperatures of the (Bi, Pb)2Sr2Ca2Cu3Ox phase under partial pressures of oxygen between 10−3 and 0.21 bar with and without additions of silver

We have investigated the stability of the (Bi, Pb)2Sr2Ca2Cu3Ox phase for the stoichiometry (Bi: Pb: Sr:Ca: Cu = 1.72: 0.34: 1.83: 1.97: 3.13), subjecting it to temperatures between 700 and 850 °C under various oxygen partial pressures. A narrow region was found in which Bi, Pb(2223) was the only superconducting phase. This region follows closely the thermal decomposition line. X-ray pure Bi, Pb(2223) will partially decompose if treated outside of the stability region. For a given oxygen partial pressure, the Bi, Pb(2223) phase tends to coexist with the 2201 phase for temperatures above, and the 2212 phase for temperatures below this region. At even lower temperatures an additional lead-rich phase appears. Critical temperatures Tc vary little with treatment and range between 108.5 K and 110.8 K. If 10% silver is added to the starting powder, the phase coexistence regions shift. Silver does not seem to have a significant effect on the absolute values of the critical temperature. The Bi, Pb(2223) thermal decomposition temperature for a given oxygen pressure is lowered by at least 10 K by the presence of Ag.