Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
Complex Assemblies of Soft Matter (COMPASS), Solvay-CNRS-UPenn UMI 3254, Bristol, Pennsylvania 19007, USA.
Nat Mater. 2015 Jan;14(1):101-8. doi: 10.1038/nmat4083. Epub 2014 Sep 14.
The microscopic kinetics of ubiquitous solid-solid phase transitions remain poorly understood. Here, by using single-particle-resolution video microscopy of colloidal films of diameter-tunable microspheres, we show that transitions between square and triangular lattices occur via a two-step diffusive nucleation pathway involving liquid nuclei. The nucleation pathway is favoured over the direct one-step nucleation because the energy of the solid/liquid interface is lower than that between solid phases. We also observed that nucleation precursors are particle-swapping loops rather than newly generated structural defects, and that coherent and incoherent facets of the evolving nuclei exhibit different energies and growth rates that can markedly alter the nucleation kinetics. Our findings suggest that an intermediate liquid should exist in the nucleation processes of solid-solid transitions of most metals and alloys, and provide guidance for better control of the kinetics of the transition and for future refinements of solid-solid transition theory.
普遍存在的固-固相转变的微观动力学仍未得到很好的理解。在这里，我们通过使用直径可调微球的胶体膜的单粒子分辨率视频显微镜，表明在方形和三角形晶格之间的转变是通过涉及液相的两步扩散形核途径发生的。由于固-液界面的能量低于各固相之间的能量，所以该形核途径优于直接的一步形核途径。我们还观察到，形核前体是粒子交换环，而不是新生成的结构缺陷，并且演化核的相干和非相干面具有不同的能量和生长速率，这可以显著改变形核动力学。我们的研究结果表明，大多数金属和合金的固-固转变的形核过程中应该存在中间液相，并为更好地控制转变的动力学以及未来对固-固转变理论的改进提供了指导。
