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

Abstract

<jats:p>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.</jats:p>

Roles of liquid structural ordering in glass transition, crystallization, and water's anomalies

“…Such crystal nucleation behavior was directly confirmed by confocal microscopy experiments in colloidal systems by Tan et al [118]. We have found that preordering also plays a critical role in the polymorph selection by simulations [116] and confocal microscopy experiments [119]. Furthermore, we have confirmed that this scenario of crystal nucleation is valid for soft spheres [120] and water [121], indicating the universality of this scenario of crystal nucleation [117].…”

Revealing thermally-activated nucleation pathways of diffusionless solid-to-solid transition

“…We use two structural order parameters, which are coarsegrained bond orientational order parameters, W 6 and Q 6 , to quantify the single-particle-level local structures (see Methods on their definitions). W 6 is used to distinguish fcc and bcc by its sign (W 6 ≥ 0 for bcc and W 6 < 0 for fcc), whereas Q 6 quantifies the degree of crystalline order of the solid (particles with Q 6 < 0.35) are regarded as defective structures, which mainly consist of highly distorted (defective) solids with a small amount of liquidlike (Q 6 < 0.25) particles 21,22,[39][40][41] (Fig. 2).…”

“…W 6 is used to distinguish fcc and bcc by its sign ( W 6 ≥ 0 for bcc and W 6 < 0 for fcc), whereas Q 6 quantifies the degree of crystalline order of the solid (particles with Q 6 < 0.35 are regarded as defective structures, which mainly consist of highly distorted (defective) solid and a amall amount of liquid-like ( Q 6 < 0.25) particles.) 21 , 22 , 39 – 41 (Fig. 2 ).…”

“…Fortunately, as an important class of soft materials, colloidal suspensions are suitable for real-space threedimensional (3D) microscopy observations. The controllability of the size, shape, and interparticle interaction of colloidal particles has provided deep microscopic insights into various phase transitions, including crystallisation [19][20][21][22] , melting 23,24 , glass transition 25 as well as solid-to-solid transitions. Concerning martensitic transitions in colloidal crystals, many studies have been performed by applying an electric field 12,26 , changing the particle shape, confinement or volume fractions 14,[27][28][29][30][31][32] , shear 33,34 and adjusting the DNA grafting 13,35 .…”

An Artificial Neural Network Reveals the Nucleation Mechanism of a Binary Colloidal AB13 Crystal

“…Several scenarios such as a classical one-step crystallization process, a nonclassical two-step crystallization mechanism with precursors consisting of local regions with either high density, high bond-orientational order, or competing orders, or a spinodal-like process have been proposed, but all of these crystallization mechanisms are still heavily debated. 1 − 10 …”