Phase stability and oxygen non-stoichiometry of SrCo0.8Fe0.2O3−δ measured by in situ neutron diffraction


McIntosh, Steven and Vente, Jaap F. and Haije, Wim G. and Blank, Dave H.A. and Bouwmeester, Henny J.M. (2006) Phase stability and oxygen non-stoichiometry of SrCo0.8Fe0.2O3−δ measured by in situ neutron diffraction. Solid State Ionics, 177 (9-10). pp. 833-842. ISSN 0167-2738

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Abstract:The phase stability, oxygen stoichiometry and expansion properties of SrCo0.8Fe0.2O3−δ (SCF) were determined by in situ neutron diffraction
between 873 and 1173 K and oxygen partial pressures of 5×10−4 to 1 atm. At a pO2 of 1 atm, SCF adopts a cubic perovskite structure, space
group Pm3¯m, across the whole temperature range investigated. At a pO2 of 10−1 atm, a two-phase region exists below 922 K, where the cubic
perovskite phase coexists with a vacancy ordered brownmillerite phase, Sr2Co1.6Fe0.4O5, space group Icmm. A pure brownmillerite phase is
present at pO2 of 10−2 and 5×10−4 atm below 1020 K. Above 1020 K, the brownmillerite phase transforms to cubic perovskite through a twophase
region with no brownmillerite structure observed above 1064 K. Large distortion of the BO6 (B=Co, Fe) octahedra is present in the
brownmillerite structure with apical bond lengths of 2.2974(4)Å and equatorial bond lengths of 1.9737(3) Å at 1021 K and a pO2 of 10−2 atm.
SCF is highly oxygen deficient with a maximum oxygen stoichiometry, 3−δ, measured in this study of 2.58(2) at 873 K and a pO2 of 1 atm and a
minimum of 2.33(2) at 1173 K and a pO2 of 5×10−4 atm. Significant differences in lattice volume and expansion behavior between the
brownmillerite and cubic perovskite phases suggest potential difficulties in thermal cycling of SrCo0.8Fe0.2O3−δ membranes
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