Stability of the cubic perovskite SrFe0.8Co0.2O3−δ

Dense ceramic bars of the perovskite material SrFe0.8Co0.2O3−δ have been synthesized by solid-state reaction and studied by in-situ neutron diffraction through the range of oxygen partial pressure (pO2) from 10−0.68 to 10−13.3 atm at 900 °C. Over the complete range, the material retains the cubic perovskite structure and is stable even when δ>0.5. Between air and log pO2=−2.3, δ increases from 0.35 to 0.44 and the lattice expands. Lowering the pO2 further leads to an oxygen content “plateau” at δ≈0.5, through a log pO2 range of −3.5 to −8.6. Below this, the lattice undergoes further expansion, as oxygen is lost, most likely when Co3+ undergoes reduction to Co2+. Rietveld analysis indicates that there is no deviation from the Fe/Co 80:20 ratio over the entire pO2 range. The behavior of this perovskite is compared to that of the perovskite phase of similar composition found in a SrFeCo0.5Oy ceramic membrane material studied under similar conditions.