Study of the Mixed‐Conducting SrFeCo 0.5 O y System

Mixed‐conducting Sr‐Fe‐Co oxides have potential applications in dense ceramic membranes for high‐purity oxygen separation and/or methane conversion to produce syngas (CO + H 2 ), because of their combined high electronic/ionic conductivity and significant oxygen permeability. SrFeCo 0.5 O y has been synthesized by the solid‐state reaction method. Conductivities were measured at elevated temperatures in various gas environments and increased as temperature and oxygen partial pressure ( p O2 ) increased in the surrounding environment. Neutron powder diffraction experiments revealed that in a high p O2 environment the SrFeCo 0.5 O y material consists of three different phases. The relative concentration of each component phase is dependent on temperature and p O2 in the surrounding environment. In air, Sr 2 (Fe, Co) 3 O y (236‐phase) is the majority phase and consists of >75 wt% of the total, whereas the perovskite and rocksalt phases account for ∼20 and <5 wt%, respectively. However, in a reducing environment, the 236‐phase decomposes and converts to perovskite and rocksalt phase at high temperature. In an environment of p O2 < 10 −12.2 atm, the 236‐phase is completely converted into perovskite (brownmillerite) and rocksalt phases.