The structure of ferrihydrite, a nanocrystalline material
The structure of ferrihydrite, a nanocrystalline material
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DOI：
10.1126/science.1142525
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发表时间：
2007-06-22
期刊：
影响因子：
56.9
通讯作者：
Parise, John B.
中科院分区：
文献类型：
--
作者：
Michel, F. Marc;Ehm, Lars;Parise, John B.
尽管水铁矿在天然沉积物中无处不在，并且作为工业吸附剂具有重要性，但这种羟基氧化铁的纳米结晶性阻碍了传统方法依赖于长程有序的准确结构测定。我们揭示了原子排列的对分布函数（PDF）的实空间建模来自直接傅立叶变换的总X射线散射。使用不同途径合成的水铁矿的PDF与单相一致（六方空间群P6（3）mc; a =类似于5.95埃，c =类似于9.06埃）。在其理想形式中，这种结构包含20%的四面体和80%的八面体配位铁，并具有与贝克-菲吉斯三角洲-Keggin簇密切相关的基本结构基序。实空间拟合表明随着颗粒尺寸的减小结构松弛，并且还表明二阶效应，如内部应变、堆垛层错和颗粒形状对PDF有贡献。
Despite the ubiquity of ferrihydrite in natural sediments and its importance as an industrial sorbent, the nanocrystallinity of this iron oxyhydroxide has hampered accurate structure determination by traditional methods that rely on long-range order. We uncovered the atomic arrangement by real-space modeling of the pair distribution function (PDF) derived from direct Fourier transformation of the total x-ray scattering. The PDF for ferrihydrite synthesized with the use of different routes is consistent with a single phase (hexagonal space group P6(3)mc; a = similar to 5.95 angstroms, c = similar to 9.06 angstroms). In its ideal form, this structure contains 20% tetrahedrally and 80% octahedrally coordinated iron and has a basic structural motif closely related to the Baker-Figgis delta-Keggin cluster. Real-space fitting indicates structural relaxation with decreasing particle size and also suggests that second-order effects such as internal strain, stacking faults, and particle shape contribute to the PDFs.