Oxygen nonstoichiometry, chemical expansion, mixed conductivity, and anodic behavior of Mo-substituted Sr<sub>3sub>Fe<sub>2sub>O<sub>7-δsub>

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• 作者：V.V. Kharton ; M.V. Patrakeev ; E.V. Tsipis ; M. Avdeev ; E.N. Naumovich ; P.V. Anikina ; J.C. Waerenborgh
• 关键词：Mixed ionic-electronic conductors ; Perovskite-related ferrites ; Oxygen intercalation ; p(O<sub>2sub>)– ; T– ; δ ; diagrams ; Point defects ; Mö ; ssbauer spectroscopy ; Dimensional stability
• 刊名：Solid State Ionics
• 出版年：2010
• 出版时间：26 July 2010
• 年：2010
• 卷：181
• 期：21-22
• 页码：1052-1063
• 全文大小：2365 K

文摘

The incorporation of molybdenum in the Ruddlesden-Popper type Sr<sub>3sub>Fe<sub>2-xsub>Mo<sub>xsub>O<sub>7-δsub> (x = 0–0.1) decreases oxygen deficiency, thermal expansion and electron-hole transport, and increases n-type electronic conductivity in reducing atmospheres. The oxygen ionic conduction remains essentially unaffected by doping. The equilibrium p(O<sub>2sub>)–T–δ diagram of Sr<sub>3sub>Fe<sub>1.9sub>Mo<sub>0.1sub>O<sub>7-δsub>, collected in oxygen partial pressure ranges from 10<sup>− 20sup> to 0.7 atm at 973–1223 K, can be adequately described by a defect model accounting for the energetic nonequivalence of apical O1 and equatorial O3 sites in the layered structure, in combination with iron disproportionation and stable octahedral coordination of Mo<sup>6+sup> and Mo<sup>5+sup> cations. The calculated enthalpy of anion exchange between the O1 and O3 positions, 0.49–0.51 eV, is in agreement with the values predicted by the atomistic computer simulation technique. The high-temperature X-ray diffraction studies showed a strongly anisotropic expansion of the Ruddlesden-Popper lattice on reduction, leading to very low chemical strains favorable for electrochemical applications. At 298–1223 K and oxygen pressures from 10<sup>− 8sup> to 0.21 atm, the linear thermal expansion coefficient of Sr<sub>3sub>Fe<sub>1.9sub>Mo<sub>0.1sub>O<sub>7-δsub> varies in the narrow range (12.9–14.2) × 10<sup>− 6sup> K<sup>− 1sup>. The relatively low level of n-type electronic conductivity leads, however, to a poor performance of porous Sr<sub>3sub>Fe<sub>1.9sub>Mo<sub>0.1sub>O<sub>7-δsub> anodes in contact with lanthanum gallate-based solid electrolyte under reducing conditions.