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首页> 外文期刊>Chemistry of Materials: A Publication of the American Chemistry Society >Defining Crystalline/Amorphous Phases of Nanoparticles through X-ray Absorption Spectroscopy and X-ray Diffraction: The Case of Nickel Phosphide
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Defining Crystalline/Amorphous Phases of Nanoparticles through X-ray Absorption Spectroscopy and X-ray Diffraction: The Case of Nickel Phosphide

机译：通过X射线吸收光谱和X射线衍射确定纳米粒子的结晶/非晶相：磷化镍的情况

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摘要

In this study we elucidate the structural distinctions between amorphous and crystalline Ni2P nanoparticles synthesized using tri-n-octylphosphine (TOP), through X-ray absorption spectroscopy (XAS), X-ray dim-action (XRD), and inductively coupled plasma (ICP). We determine the differences in their chemical and atomic structure, which have not been previously reported, yet are essential for understanding their potential as nanocatalysts. These structural characteristics are related to the corresponding nanoparticle magnetic properties analyzed by performing magnetic measurements. XAS results reveal a significant P concentration in the amorphous nanoparticle sample - placing the stoichiometry close to NijP - despite XRD results that show only fcc Ni contributions. By comparing the long-range structural order from XRD to the short-range radial structure from EXAFS we conclude that both techniques are necessary to obtain a complete structural picture of amorphous and crystalline nanoparticle phases due to the limitations of XRD amorphous characterization. We find that phases are amorphous with respect to XRD when their offsets (deviations) from bulk interatomic distances have a standard deviation as high as ~4.82. Phases with lower standard deviation (e.g., <1.22), however, are detectable as crystalline through XRD. The possible presence of amorphous phases should be considered when using XRD alone for nanoparticle characterization. This is particularly important when highly reactive reagents such as TOP are used in synthesis. By characterizing amorphous nickel phosphide nanoparticles that have a comparable stoichiometry to Ni2P, we confirm that TOP serves as a highly effective phosphorus source, even at temperatures as low as 230 °C. Unintended amorphous structure domains may significantly affect nanoparticle properties, and in turn, their functionality.
机译：在这项研究中，我们通过X射线吸收光谱法（XAS），X射线暗作用（XRD）和感应耦合等离子体，阐明了使用三正辛基膦（TOP）合成的无定形和结晶Ni2P纳米颗粒之间的结构区别（ ICP）。我们确定了它们在化学和原子结构上的差异，这些差异先前未曾报道过，但对于理解其作为纳米催化剂的潜力至关重要。这些结构特征与通过进行磁性测量分析的相应的纳米颗粒磁性有关。尽管XRD结果仅显示了fcc Ni的贡献，但XAS结果显示出非晶态纳米颗粒样品中P的浓度很高-使化学计量接近NijP。通过比较XRD的长程结构顺序和EXAFS的短程径向结构，我们得出结论，由于XRD非晶态表征的局限性，两种技术对于获得非晶和结晶纳米粒子相的完整结构图都是必需的。我们发现，当相距整体原子间距的偏移（偏差）具有高达〜4.82的标准偏差时，相对于XRD而言，相是非晶态的。然而，具有较低标准偏差（例如，＜1.22）的相可以通过XRD检测为结晶。当单独使用XRD进行纳米颗粒表征时，应考虑非晶相的可能存在。当高反应性试剂（例如TOP）用于合成时，这尤其重要。通过表征化学计量与Ni2P相当的非晶态磷化镍纳米颗粒，我们证实即使在低至230°C的温度下，TOP仍可作为高效磷源。意外的非晶结构域可能会严重影响纳米粒子的性能，进而影响其功能。

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