Many complex intermetallic structures feature a curious juxtaposition of domains with strict 3D periodicity and regions of much weaker order or incommensurability. This article explores the basic principles leading to such arrangements through an investigation of the weakly ordered channels of Fe2Al5. It starts by experimentally confirming the earlier crystallographic model of the high-temperature form, in which nearly continuous columns of electron density corresponding to disordered Al atoms emerge. Then electronic structure calculations on ordered models are used to determine the factors leading to the formation of these columns. These calculations reveal electronic pseudogaps near 16 electrons/Fe atom, an electron concentration close to the Al-rich side of the phase's homogeneity range. Through a reversed approximation Molecular Orbital (raMO) analysis, these pseudogaps are correlated with the filling of 18-electron configurations on the Fe atoms with the support of isolobal σ Fe–Fe bonds. The resulting preference for 16 electrons/Fe requires a fractional number of Al atoms in the Fe2Al5unit cell. Density functional theory–chemical pressure (DFT-CP) analysis is then applied to investigate how this nonstoichiometry is accommodated. The CP schemes reveal strong quadrupolar distributions on the Al atoms of the channels, suggestive of soft atomic motions along the undulating electron density observed in the Fourier map that allow the Al positions to shift easily in response to compositional changes. Such a combination of preferred electron counts tied to stoichiometry and continuous paths of CP quadrupoles could provide predictive indicators for the emergence of channels of disordered or incommensurately spaced atoms in intermetallic structures.

中文翻译：

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金属间化合物中弱有序域的原理：Fe2Al5 中原子堆积和电子的协同效应


许多复杂的金属间结构具有严格的 3D 周期性域和秩序较弱或不可通约性区域的奇怪并置。本文通过研究 Fe2Al5 的弱有序通道，探讨了导致这种排列的基本原理。首先通过实验证实了高温形式的早期晶体学模型，其中出现了与无序铝原子相对应的几乎连续的电子密度柱。然后使用有序模型的电子结构计算来确定导致这些柱形成的因素。这些计算揭示了接近 16 个电子/Fe 原子的电子赝能隙，电子浓度接近相均匀性范围的富铝一侧。通过反向近似分子轨道 (raMO) 分析，这些赝能隙与在等瓣 σ Fe-Fe 键支持下 Fe 原子上 18 电子构型的填充相关。由此产生的对 16 个电子/Fe 的偏好需要 Fe2Al5 晶胞中的分数数量的 Al 原子。然后应用密度泛函理论-化学压力（DFT-CP）分析来研究如何适应这种非化学计量。 CP方案揭示了通道的Al原子上的强四极分布，这表明沿着傅立叶图中观察到的波动电子密度的软原子运动，使得Al位置可以轻松地响应成分变化而移动。这种与化学计量和 CP 四极的连续路径相关的优选电子计数的组合可以为金属间结构中无序或不相称间隔原子通道的出现提供预测指标。