Revealing roles of competing local structural orderings in crystallization of polymorphic systems

Most systems have more than two stable crystalline states in the phase diagram, which is known as polymorphism. Crystallization in such a system is often under strong influence of competing orderings linked to those crystals. However, how such competition affects crystal nucleation and ordering toward the final crystalline state is largely unknown. This is primarily because the competition takes place locally and thus is masked by large positional fluctuations. We develop a unique method to correctly identify local symmetries by removing their distortions due to positional fluctuations. This allows us to experimentally access the spatiotemporal fluctuations of local symmetries at a single-particle level in crystallization of a charged colloidal system near the body-centered cubic-face-centered cubic border. Thus, we successfully reveal the crucial roles of competing ordering in the initial selection of polymorphs and the final grain boundary motion toward the most stable state from a microscopic perspective.

大多数体系在相图中具有两种以上的稳定晶态，这被称为多晶型现象。在这样的体系中，结晶过程往往受到与这些晶体相关的竞争序的强烈影响。然而，这种竞争如何影响晶体成核以及向最终晶态的有序化在很大程度上是未知的。这主要是因为竞争是在局部发生的，因此被较大的位置涨落所掩盖。我们开发了一种独特的方法，通过消除位置涨落导致的畸变来正确识别局部对称性。这使我们能够在实验上获取体心立方 - 面心立方边界附近的带电胶体体系结晶过程中单个粒子层面上局部对称性的时空涨落。因此，我们从微观角度成功揭示了竞争序在多晶型的初始选择以及最终晶界向最稳定状态运动中的关键作用。