Phase stability of SrFeCo0.5Oy under synthesis and annealing conditions

Dense ceramic tubes of the multi phase mixed ionic/electronic conductor SrFeCo0.5Oy (SFC2) have been .synthesized by solid-state reaction. Stability of the component phases of SFC2 was studied by insitu neutron diffraction in the temperature range of 900–1200 °C in air and Ar environments. In air between 900 and 1050 °C, the material is stable, with Sr2(Fe,Co)3Oy (236) being the major phase. Above 1050 °C, 236 undergoes decomposition into perovskite and rocksalt phases, and at 1200 °C, only a small fraction of the 236 phase is stable. In Ar, the 236 phase is completely stable at 900 °C but is completely decomposed by 1100 °C, whereupon only the perovskite and rocksalt phases remain. Rietveld analysis indicates that the 236 and perovskite phases become more Fe-rich as decomposition occurs, while the perovskite phase lattice parameter and oxygen content vary readily as temperature and gas environment are changed.