通过密度泛函理论计算对铁基氧化物的 K-Edge XANES 研究,The Journal of Physical Chemistry C

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通过密度泛函理论计算对铁基氧化物的 K-Edge XANES 研究
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2021-11-18 , DOI: 10.1021/acs.jpcc.1c08461
Jing Zhu ₁ , Zhenhua Zeng ₂ , Wei-Xue Li _{1,

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Affiliation

X 射线吸收光谱 (XAS) 是一种强大的技术，可同时表征工作催化剂和电池材料等的氧化态和局部结构。然而，由于光谱对多种因素的高度敏感性，通过 XAS 破译表观氧化态仍然具有挑战性。在这里，一系列铁基催化剂和电池电极的X射线吸收近边结构（XANES）光谱的综合第一性原理计算，包括FeO、Fe ₂ O ₃、Fe(OH) ₂、FeOOH、FeAl ₂ O ₄和 MFeO ₂(M = Li、Na 或 K)，通过剖析 XANES 线形状对详细电子和几何结构的依赖性来阐明这个问题。我们发现，与通常从 XAS 测量中提取的成分和因素（即氧化态和局部结构）相比，不能从 XAS 实验中直接获得的非局部结构（例如，晶体结构）是 XANES 的主要因素。主边缘、主峰和柱状图的线条形状。正如通过具有相同或相似非局域结构的 Fe 化合物所证明的那样，它们的线条形状相似，并且随着化学环境的变化而变化。另一方面，我们发现局部配位（八面体与四面体）和氧化态分别在前边缘的强度和前边缘与主边缘之间的能量分裂上占主导地位。我们证明，阐明这些控制因素和起源不仅为可靠分配光谱和理解半经验规则提供了有价值的见解，而且还揭示了 XAS 测量中无法直接访问的结构信息。

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K-Edge XANES Investigation of Fe-Based Oxides by Density Functional Theory Calculations

X-ray absorption spectroscopy (XAS) is a powerful technique for simultaneously characterizing the oxidation states and local structures of working catalysts and battery materials, among others. However, deciphering the apparent oxidation state through XAS remains challenging because of the high sensitivity of spectra to multiple factors. Here, comprehensive first-principles calculations of X-ray absorption near-edge structure (XANES) spectra of a series of Fe-based catalysts and battery electrodes, including FeO, Fe₂O₃, Fe(OH)₂, FeOOH, FeAl₂O₄, and MFeO₂ (M = Li, Na, or K), were performed to shed light on the issue by dissecting the dependence of XANES line shapes on detailed electronic and geometric structures. We revealed that, in comparison with the composition and factors usually extracted from XAS measurements (i.e., the oxidation state and local structure), nonlocal structures (e.g., crystal structure) that cannot be straightforwardly obtained from XAS experiments are more dominant factors of the XANES line shapes of the main edge, main peak, and postedge. As demonstrated through Fe compounds with the same or similar nonlocal structures, their line shapes are alike and shift in response to a change in the chemical environment. On the other hand, we found that the local coordination (octahedra vs tetrahedra) and the oxidation state are more dominant on the intensity of the pre-edge and the energy splitting between the pre-edge and the main edge, respectively. We demonstrated that clarifying these control factors and origins not only provides valuable insights into reliable assignment of spectra and understanding semiempirical rules but also unravels the structural information that is not directly accessible in XAS measurements.

更新日期：2021-12-02

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