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首页> 外文期刊>RSC Advances >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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Structural investigations of La0.6Sr0.4FeO3?δ under reducing conditions: kinetic and thermodynamic limitations for phase transformations and iron exsolution phenomena

机译：La 0.6 Sr 0.4 FeO 3？δ 在还原条件下的结构研究：相变的动力学和热力学极限和铁释放现象

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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 (Rc to Pmm) 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.
机译：一系列缺氧镧锶铁氧体（La 0.6 Sr 0.4 FeO 3？δ ，LSF）样品在各种惰性和还原条件下（最高温度为873 K）以了解其氧和铁缺乏在这两个过程中的作用。铁的溶出发生在较高温度的还原性环境中，导致在表面形成铁棒或颗粒。利用多种原位和原位方法（原位 X射线衍射（XRD），原位热重法分析（TGA）和扫描X射线吸收近边缘光谱（XANES）），据此评估了热力学和动力学限制。铁溶出之前，钙钛矿经历了衍射峰到较小的2 θ角的非线性移动，这可以归因于菱形到立方（ R <从em> c 到 Pm m ）的结构过渡。在还原性气氛中，立方结构在冷却至室温时稳定，而在氧化条件下抑制了转变。这表明晶格中氧空位的积累稳定了立方相。示出的解出物本身表现出扩散受限的Avrami样行为，其中铁向贫铁表面附近区域的运输是限速步骤。

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