Stability of the cubic perovskite SrFe sub(0.8)Co sub(0.2)O sub(3- delta )

Dense ceramic bars of the perovskite material SrFe sub(0.8)Co sub(0.2)O sub(3- delta ) have been synthesized by solid-state reaction and studied by in-situ neutron diffraction through the range of oxygen partial pressure (pO sub(2)) from 10 super(-0.68) to 10 super(-13.3) atm at 900 degree C. Over the complete range, the material retains the cubic perovskite structure and is stable even when delta > 0.5. Between air and log pO sub(2) = -2.3, delta increases from 0.35 to 0.44 and the lattice expands. Lowering the pO sub(2) further leads to an oxygen content "plateau" at delta approximately 0.5, through a log pO sub(2) range of -3.5 to -8.6. Below this, the lattice undergoes further expansion, as oxygen is lost, most likely when Co super(3+) undergoes reduction to Co super(2+). Rietveld analysis indicates that there is no deviation from the Fe/Co 80:20 ratio over the entire pO sub(2) range. The behavior of this perovskite is compared to that of the perovskite phase of similar composition found in a SrFeCo sub(0.5)O sub(y) ceramic membrane material studied under similar conditions. copyright 2002 Elsevier Science B.V. All rights reserved.