Nonclassical Crystal Growth Research Articles

Nanoparticle-mediated nonclassical crystal growth of sodium fluorosilicate nanowires and nanoplates

We observed nonclassical crystal growth of the sodium fluorosilicate nanowires, nanoplates, and hierarchical structures through self-assembly and aggregation of primary intermediate nanoparticles. Unlike traditional ion-by-ion crystallization, the primary nanoparticles formed first and their subsequent self-assembly, fusion, and crystallization generated various final crystals. These findings offer direct evidences for the aggregation-based crystallization mechanism.

Quantifying the Kinetics of Crystal Growth by Oriented Aggregation

AbstractOriented aggregation is a nonclassical crystal growth mechanism resulting in new secondary particles composed of crystallographically aligned primary crystallites. These secondary crystals often have unique and symmetry-defying morphologies, can be twinned, and can contain stacking faults and other significant defects. A wide range of materials, such as titanium dioxide, iron oxides, selenides and sulfides, and metal oxyhydroxides, are known to grow by oriented aggregation under certain conditions. Evidence for oriented aggregation also has been observed in natural materials. Over the last decade, reports of this crystal growth mechanism have appeared with increasing frequency in the scientific literature. The development of kinetic models aimed at improving our fundamental understanding as well as facilitating purposeful control over size, size distribution, and shape has ranged from simple dimer formation models to polymeric models and population balance models. These models have enabled detection and characterization of crystal growth by oriented aggregation using methods such as small-angle x-ray scattering, among others, in addition to transmission electron microscopy. As our fundamental understanding of oriented aggregation improves, novel and complex functional materials are expected to emerge. This article presents a summary of some recent results, methods, and models for characterizing crystal growth by oriented aggregation.

A Facile Synthesis of Uniform NH4TiOF3Mesocrystals and Their Conversion to TiO2Mesocrystals

Uniform mesocrystals of TiO2 (anatase) have been prepared from mesocrystals of NH4TiOF3. NH4TiOF3 was synthesized from an aqueous solution containing (NH4)2TiF6 and H3BO3 in the presence of a nonionic surfactant Brij 56, Brij 58, or Brij 700, at low temperatures. The exterior shapes of NH4TiOF3 mesocrystals can be tuned by adjusting the reagent concentration, reaction time, reaction temperature, and rate of stirring. The formation of the NH4TiOF3 mesocrystals proceeds via a self-assembly process involving nonclassical crystal growth. By sintering in air at 450 degrees C, or washing with H3BO3 solution at ambient temperatures, the NH4TiOF3 mesocrystals can be converted to mesocrystals of TiO2 (anatase), and the original architecture is retained.

Size dependent kinetics of oriented aggregation

Oriented aggregation is an important, nonclassical crystal growth mechanism by which nanocrystals grow, defects are formed, and unique—often symmetry-defying—crystal morphologies can be produced. This growth mechanism involves the irreversible and crystallographically specific self-assembly of primary nanocrystals and results in the formation of new single crystals, twins, and intergrowths. This paper presents data showing that growth by oriented aggregation is consistent with second-order kinetics with respect to the concentration of the primary nanoparticles and demonstrates that the overall rate constant for growth by oriented aggregation increases dramatically with decreasing primary particle size. Results are discussed in the context of DLVO interactions. The experimental results explain the common observation that growth by oriented aggregation slows as a function of continued crystal growth.

Growth of Prussian Blue Microcubes under a Hydrothermal Condition: Possible Nonclassical Crystallization by a Mesoscale Self-Assembly

A classical crystallization process starts from stable nuclei followed by a simple enlargement of the nuclei by unit-cell replication. In recent years, the universality of such classical crystallization has been questioned upon investigations of biomineralization processes, and there are few examples showing that crystal growth may not follow such a classical crystallization process. In this paper, a typical coordination polymer, Prussian blue microcrystals, has been synthesized under hydrothermal conditions. By carefully analyzing the intermediates during the crystal growth process, we found that the growth of Prussian blue under the given growth conditions may follow a nonclassical crystal growth process in which a mesoscale self-assembly of nanocrystallites is included during crystal growth. Such a mesoscale self-assembly process could be a common phenomenon for growth of some crystals with extremely low solubility.

Regular perturbation expansion solution for steady nonclassical needle crystal growth

The present paper is concerned with the steady, dendrite growth from a pure melt with arbitrary undercooling parameter (−1< T ∞<0). We formulated and discussed the so-called steady nonclassical needle crystal growth problem, described the regular perturbation expansion (RPE) solution in terms of the small surface tension parameter ε 2 and also carried out extensive computation for their numerical results.