Andersen Henrik L, Christensen Mogens
Center for Materials Crystallography, Department of Chemistry and iNANO, Langelandsgade 140, DK-8000 Aarhus C, Denmark.
Nanoscale. 2015 Feb 28;7(8):3481-90. doi: 10.1039/c4nr06937d.
The evolution of size and size distribution during hydrothermal synthesis of nanocrystalline CoFe2O4 has been studied by in situ synchrotron powder X-ray diffraction (PXRD). Varying synthesis temperature or [OH(-)] concentration in the precursor proves to have no significant effect on the final volume-weighted nanocrystallite sizes (∼12 nm) of CoFe2O4. However, analysis by whole powder pattern modeling of the [OH(-)] concentration series reveals a substantial difference in the number-weighted size distributions when varying the amount of base used. Furthermore, changing the metal ion concentration prior to NaOH addition in the precursor preparation gives a handle to control the nanoparticle sizes (∼5-15 nm). All in situ experiments show almost instantaneous formation of the CoFe2O4 nanocrystallites, without significant growth or broadening of the size distribution after 60 s. Magnetic hysteresis curve measurements illustrate, how this facilitates the tailoring of materials with specific magnetic properties, as larger particles (∼15 nm) exhibit hard magnetic properties while the smaller particles (∼6-7 nm) are superparamagnetic.
通过原位同步辐射粉末X射线衍射（PXRD）研究了纳米晶CoFe₂O₄水热合成过程中尺寸和尺寸分布的演变。结果表明，改变合成温度或前驱体中的[OH⁻]浓度对CoFe₂O₄最终的体积加权纳米微晶尺寸（约12 nm）没有显著影响。然而，通过对[OH⁻]浓度系列的全粉末图案建模分析发现，改变碱的用量时，数均尺寸分布存在显著差异。此外，在前驱体制备中，在加入NaOH之前改变金属离子浓度可以控制纳米颗粒的尺寸（约5-15 nm）。所有原位实验均表明，CoFe₂O₄纳米微晶几乎瞬间形成，60 s后尺寸分布没有明显增长或变宽。磁滞曲线测量表明，这有助于定制具有特定磁性的材料，因为较大的颗粒（约15 nm）表现出硬磁性能，而较小的颗粒（约6-7 nm）是超顺磁性的。
