Department of Chemistry, University of Waterloo , 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
J Am Chem Soc. 2015 Jan 28;137(3):1101-8. doi: 10.1021/ja5094056. Epub 2015 Jan 13.
Controlling the crystal structure of transparent metal oxides is essential for tailoring the properties of these polymorphic materials to specific applications. The structural control is usually done via solid state phase transformation at high temperature or pressure. Here, we report the kinetic study of in situ phase transformation of In2O3 nanocrystals from metastable rhombohedral phase to stable cubic phase during their colloidal synthesis. By examining the phase content as a function of time using the model fitting approach, we identified two distinct coexisting mechanisms, surface and interface nucleation. It is shown that the mechanism of phase transformation can be controlled systematically through modulation of temperature and precursor to solvent ratio. The increase in both of these parameters leads to gradual change from surface to interface nucleation, which is associated with the increased probability of nanocrystal contact formation in the solution phase. The activation energy for surface nucleation is found to be 144 ± 30 kJ/mol, very similar to that for interface nucleation. Despite the comparable activation energy, interface nucleation dominates at higher temperatures due to increased nanocrystal interactions. The results of this work demonstrate enhanced control over polymorphic nanocrystal systems and contribute to further understanding of the kinetic processes at the nanoscale, including nucleation, crystallization, and biomineralization.
控制透明金属氧化物的晶体结构对于根据特定应用来调整这些多晶材料的性能至关重要。通常通过高温或高压下的固态相转变来实现结构控制。在此，我们报告了在胶体合成过程中，氧化铟纳米晶从亚稳的菱方相到稳定的立方相的原位相变的动力学研究。通过使用模型拟合方法研究不同时间的相含量，我们确定了两种不同的共存机制，即表面和界面成核。结果表明，通过调节温度和前体与溶剂的比例，可以系统地控制相变机制。这两个参数的增加导致从表面成核到界面成核的逐渐转变，这与溶液相中纳米晶接触形成的概率增加有关。表面成核的活化能为 144 ± 30 kJ/mol，与界面成核非常相似。尽管活化能相当，但由于纳米晶之间相互作用的增强，界面成核在较高温度下占主导地位。这项工作的结果表明对多晶纳米晶系统的控制得到了增强，并有助于进一步了解纳米尺度的动力学过程，包括成核、结晶和生物矿化。
