Oxygen nonstoichiometry and thermodynamic quantities in the Ruddlesden-Popper oxides LaxSr3 - xFe2O7 - δ

Yihan Ling, Fang Wang, Yusuke Okamoto, Takashi Nakamura, Koji Amezawa

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    14 Citations (Scopus)

    Abstract

    Oxygen nonstoichiometry in the Ruddlesden-Popper type oxides LaxSr3 - xFe2O7 - δ (x = 0, 0.25 and 0.5) was determined by means of the high temperature gravimetry and the coulometric titration. The measurements were carried out in the temperature range between 773 and 1073 K and the P(O2) range between 10-40 and 1 bar. The P(O2) dependencies of the oxygen nonstoichiometry exhibited typical plateaus at δ ∼ 1.0 for Sr3Fe2O7 - δ, δ ∼ 0.875 for La0.25Sr2.75Fe2O7 - δ and δ ∼ 0.75 for La0.5Sr2.5Fe2O7 - δ, where the average oxidation state of iron is 3 +. In the LaxSr3 - xFe2O7 - δ series, La0.5Sr2.5Fe2O7 - δ showed the smallest oxygen nonstoichiometry and was the most thermochemically stable compound against on P(O2), temperature, and the La content. Thermodynamic quantities of the partial molar enthalpy of oxygen, hO - hO°, and the partial molar entropy of oxygen, sO - sO°, were calculated from measured nonstoichiometric data. The behavior of oxygen nonstoichiometry and thermodynamic quantities indicates that the ideal-solution-like defect formation is established (La,Sr)3Fe2O7 in the oxygen deficient region.

    Original languageEnglish
    Pages (from-to)298-302
    Number of pages5
    JournalSolid State Ionics
    Volume288
    DOIs
    Publication statusPublished - 2016 May 1

    Keywords

    • Coulometric titration
    • Oxygen nonstoichiometry
    • Ruddlesden-Popper oxides
    • Thermodynamic quantities

    ASJC Scopus subject areas

    • Chemistry(all)
    • Materials Science(all)
    • Condensed Matter Physics

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