The effects of oxygen partial pressure (po2)and temperature on the oxygen content, structure, and phase stability of Pb2Sr2YCu3O8+δ, Pb2Sr2GdCu3O8+δ, Pb2Sr2Y0.60Ca0.40Cu3O8+δand Pb2Sr2YCu2 50Ag0.50O8+δ are determined. In the range 300–600 °C the compounds with δ = 0 are reversibly oxidized to δ as high as ≈1.6. The extent of this reaction depends on the heating rate as well as the temperature and PO2. The structure changes from orthorhombic to tetragonal, and the unit cell expands on oxidation. The oxygen content in the phase passes through a maximum around 500 °C. Above ~630 °C an irreversible oxidative decomposition occurs depending on the Po2 and nature of the substitutions. The initial decomposition product is a pseudocubic perovskite material, but at still higher oxygen contents a SrPbO3-like perovskite forms. At lower PO2where this decomposition does not occur, the original structure undergoes a higher order transformation from orthorhombic to tetragonal symmetry near 750 °C. At temperatures ≳850 °C the oxidized products lose 02 and revert to the original phase and oxygen content. Quenching from above 850 °C or slowly cooling in decreased Po2 can be used to synthesize the orthorhombic structure with δ = 0. The nature and extent of the particular substitutions determine the exact conditions required for various oxygen contents, structures, and phase stability.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Materials Chemistry