Phase stability limits and solid-state decomposition of Bi₂Sr₂CaCu₂O_8+δ and Bi₂Sr₂Ca₂Cu₃O_10+δ in reduced oxygen pressures

We measured the phase stability of the Bi2Sr2CaCu2O8+δ and Bi2Sr2Ca2Cu3O10+δ superconductors as a function of temperature and oxygen pressure. Below the solidus temperature of ∼790°C, Bi2Sr2CaCu2O8+δ is stable at oxygen pressures one fourth of those where CuO becomes metastable, while Bi2Sr2Ca2Cu3O10+δ is stable at the same pressures where CuO is stable. Above the solidus temperature, the pressure required to stabilize either phase increases rapidly with temperature. The major solid-state decomposition products of Bi2Sr2CaCu2O8+δ are Bi2Sr3-xCaxO6+δ and Cu2O, and also Bi2Sr 2-xCaxO5 for bismuth-rich samples. For Bi2Sr2Ca2Cu3O10+δ the major decomposition products are Bi2Sr2CaCu2O8+δ, Ca2-xSrxCuO 3, and Cu2O. The solid-state decomposition reaction is reversible for the Bi-2212 phase, but not for the Bi-2223 phase. © 1993.