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Issue 6, 2018, Issue in Progress
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Structural investigations of La0.6Sr0.4FeO3−δ under reducing conditions: kinetic and thermodynamic limitations for phase transformations and iron exsolution phenomena

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Abstract

The crystal structure changes and iron exsolution behavior of a series of oxygen-deficient lanthanum strontium ferrite (La0.6Sr0.4FeO3−δ, LSF) samples under various inert and reducing conditions up to a maximum temperature of 873 K have been investigated to understand the role of oxygen and iron deficiencies in both processes. Iron exsolution occurs in reductive environments at higher temperatures, leading to the formation of Fe rods or particles at the surface. Utilizing multiple ex situ and in situ methods (in situ X-ray diffraction (XRD), in situ thermogravimetric analysis (TGA), and scanning X-ray absorption near-edge spectroscopy (XANES)), the thermodynamic and kinetic limitations are accordingly assessed. Prior to the iron exsolution, the perovskite undergoes a nonlinear shift of the diffraction peaks to smaller 2θ angles, which can be attributed to a rhombohedral-to-cubic (R[3 with combining macron]c to Pm[3 with combining macron]m) structural transition. In reducing atmospheres, the cubic structure is stabilized upon cooling to room temperature, whereas the transition is suppressed under oxidizing conditions. This suggests that an accumulation of oxygen vacancies in the lattice stabilize the cubic phase. The exsolution itself is shown to exhibit a diffusion-limited Avrami-like behavior, where the transport of iron to the Fe-depleted surface-near region is the rate-limiting step.

Graphical abstract: Structural investigations of La0.6Sr0.4FeO3−δ under reducing conditions: kinetic and thermodynamic limitations for phase transformations and iron exsolution phenomena

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Publication details

The article was received on 10 Nov 2017, accepted on 09 Jan 2018 and first published on 15 Jan 2018


Article type: Paper
DOI: 10.1039/C7RA12309D
Citation: RSC Adv., 2018,8, 3120-3131
  • Open access: Creative Commons BY license
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    Structural investigations of La0.6Sr0.4FeO3−δ under reducing conditions: kinetic and thermodynamic limitations for phase transformations and iron exsolution phenomena

    T. Götsch, L. Schlicker, M. F. Bekheet, A. Doran, M. Grünbacher, C. Praty, M. Tada, H. Matsui, N. Ishiguro, A. Gurlo, B. Klötzer and S. Penner, RSC Adv., 2018, 8, 3120
    DOI: 10.1039/C7RA12309D

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