Department of Chemistry and Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
J Am Chem Soc. 2012 Apr 25;134(16):7015-24. doi: 10.1021/ja211627r. Epub 2012 Apr 10.
The kinetics of phase transformation of colloidal In(2)O(3) nanocrystals (NCs) during their synthesis in solution was explored by a combination of structural and spectroscopic methods, including X-ray diffraction, transmission electron microscopy, and extended X-ray absorption fine structure spectroscopy. Johnson-Mehl-Avrami-Erofeyev-Kholmogorov (JMAEK) and the interface nucleation models were used to analyze the isothermal kinetic data for the phase transformation of NCs in the temperature range of 210-260 °C. The results show that NCs are initially stabilized in the metastable corundum (rh-In(2)O(3)) phase. The phase transformation occurs via nucleation of cubic bixbyite (bcc-In(2)O(3)) phase at the interface between contacting rh-In(2)O(3) NCs, and propagates rapidly throughout the NC volume. The activation energy of the phase transformation was determined from the Arrhenius expression to be 152 ± 60 kJ/mol. The interface nucleation rate is maximal at the beginning of the phase transformation process, and decreases over the course of the reaction due to a decrease in the concentration of rh-In(2)O(3) NCs in the reaction mixture. In situ high-temperature XRD patterns collected during nonisothermal treatment of In(2)O(3) NCs reveal that phase transformation of smaller NCs occurs at a faster rate and lower temperature, which is associated with their higher packing density and contact formation probability. Because NC surfaces and interfaces play a key role in phase transformation, their control through the synthesis conditions and reaction kinetics is an effective route to manipulate NC structure and properties.
通过结构和光谱方法（包括 X 射线衍射、透射电子显微镜和扩展 X 射线吸收精细结构光谱学）的组合，研究了胶体 In(2)O(3)纳米晶体（NCs）在溶液中合成过程中相转变的动力学。约翰逊-梅尔-阿夫拉米-埃罗菲耶夫-科尔莫戈罗夫（JMAEK）和界面成核模型被用于分析 210-260°C 温度范围内 NCs 相转变的等温动力学数据。结果表明，NCs 最初稳定在亚稳刚玉（rh-In(2)O(3)）相中。相转变通过在接触 rh-In(2)O(3) NC 界面处立方金红石（bcc-In(2)O(3)）相的成核发生，并迅速在 NC 体积中传播。相转变的活化能通过阿雷尼乌斯表达式确定为 152±60 kJ/mol。相转变过程开始时界面成核速率最大，随着反应的进行，由于反应混合物中 rh-In(2)O(3) NC 的浓度降低，其速率降低。在非等温处理 In(2)O(3) NC 期间收集的原位高温 XRD 图谱表明，较小 NC 的相转变发生在更快的速率和更低的温度下，这与其更高的堆积密度和接触形成概率有关。由于 NC 表面和界面在相转变中起着关键作用，因此通过合成条件和反应动力学来控制它们是控制 NC 结构和性能的有效途径。
