Phase stability limits and solid-state decomposition of Bi 2Sr 2CaCu 2O 8+δ and Bi 2Sr 2Ca 2Cu 3O 10+δ in reduced oxygen pressures

Abstract

We measured the phase stability of the Bi 2Sr 2CaCu 2O 8+δ and Bi 2Sr 2Ca 2Cu 3O 10+δ superconductors as a function of temperature and oxygen pressure. Below the solidus temperature of ∼790°C, Bi 2Sr 2CaCu 2O 8+δ is stable at oxygen pressures one fourth of those where CuO becomes metastable, while Bi 2Sr 2Ca 2Cu 3O 10+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 Bi 2Sr 2CaCu 2O 8+δ are Bi 2Sr 3− x Ca x O 6+δ and Cu 2O, and also Bi 2Sr 2− x Ca x O 5 for bismuth-rich samples. For Bi 2Sr 2Ca 2Cu 3O 10+δ the major decomposition products are Bi 2Sr 2CaCu 2O 8+δ, Ca 2− x Sr x CuO 3, and Cu 2O. The solid-state decomposition reaction is reversible for the Bi-2212 phase, but not for the Bi-2223 phase.