Aalling-Frederiksen Olivia, Pittkowski Rebecca K, Anker Andy S, Quinson Jonathan, Klemeyer Lars, Frandsen Benjamin A, Koziej Dorota, Jensen Kirsten M Ø
University of Copenhagen, Department of Chemistry, Nanoscience Center 2100 Copenhagen Ø Denmark
Aarhus University, Department of Biological and Chemical Engineering 8200 Aarhus Denmark.
Nanoscale Adv. 2024 Sep 16;6(23):5939-48. doi: 10.1039/d4na00590b.
We here investigate how the synthesis method affects the crystallite size and atomic structure of cobalt iron oxide nanoparticles. By using a simple solvothermal method, we first synthesized cobalt ferrite nanoparticles of 2 and 7 nm, characterized by Transmission Electron Microscopy (TEM), Small Angle X-ray scattering (SAXS), X-ray and neutron total scattering. The smallest particle size corresponds to only a few spinel unit cells. Nevertheless, Pair Distribution Function (PDF) analysis of X-ray and neutron total scattering data shows that the atomic structure, even in the smallest nanoparticles, is well described by the spinel structure, although with significant disorder and a contraction of the unit cell parameter. These effects can be explained by the surface oxidation of the small nanoparticles, which is confirmed by X-ray near edge absorption spectroscopy (XANES). Neutron total scattering data and PDF analysis reveal a higher degree of inversion in the spinel structure of the smallest nanoparticles. Neutron total scattering data also allow magnetic PDF (mPDF) analysis, which shows that the ferrimagnetic domains correspond to 80% of the crystallite size in the larger particles. A similar but less well-defined magnetic ordering was observed for the smallest nanoparticles. Finally, we used a co-precipitation synthesis method at room temperature to synthesize ferrite nanoparticles similar in size to the smallest crystallites synthesized by the solvothermal method. Structural analysis with PDF demonstrates that the ferrite nanoparticles synthesized this method exhibit a significantly more defective structure compared to those synthesized a solvothermal method.
我们在此研究合成方法如何影响钴铁氧化物纳米颗粒的微晶尺寸和原子结构。通过使用一种简单的溶剂热法，我们首先合成了2纳米和7纳米的钴铁氧体纳米颗粒，并用透射电子显微镜（TEM）、小角X射线散射（SAXS）、X射线和中子全散射对其进行了表征。最小的粒径仅对应于少数几个尖晶石晶胞。然而，对X射线和中子全散射数据的对分布函数（PDF）分析表明，即使是最小的纳米颗粒，其原子结构也能用尖晶石结构很好地描述，尽管存在明显的无序和晶胞参数的收缩。这些效应可以通过小纳米颗粒的表面氧化来解释，这一点通过X射线近边吸收光谱（XANES）得到了证实。中子全散射数据和PDF分析揭示了最小纳米颗粒的尖晶石结构中更高程度的反演。中子全散射数据还允许进行磁性PDF（mPDF）分析，结果表明在较大颗粒中，亚铁磁畴对应于微晶尺寸的80%。对于最小的纳米颗粒，观察到了类似但不太明确的磁有序。最后，我们在室温下使用共沉淀合成法合成了与通过溶剂热法合成的最小微晶尺寸相似的铁氧体纳米颗粒。用PDF进行的结构分析表明，与通过溶剂热法合成的铁氧体纳米颗粒相比，用这种方法合成的铁氧体纳米颗粒表现出明显更有缺陷的结构。
