Free-energy landscape of nucleation with an intermediate metastable phase studied using capillarity approximation

Iwamatsu, Masao

doi:10.1063/1.3583641

Cited by 24 publications

(69 citation statements)

References 45 publications

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“…However, Ref. [19] argued that there were cases where the FES has two independent channels leading out of the metastable phase, in contrast to our results, where we find only one. Further, Ref.…”

Section: Relationship To Previous Modelling Of Two-step Nucle-ationcontrasting

confidence: 99%

Phase transitions in fluctuations and their role in two-step nucleation

James

Beairsto

Hartt

et al. 2019

The Journal of Chemical Physics

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We consider the thermodynamic behavior of local fluctuations occurring in a stable or metastable bulk phase. For a system with three or more phases, a simple analysis based on classical nucleation theory predicts that small fluctuations always resemble the phase having the lowest surface tension with the surrounding bulk phase, regardless of the relative chemical potentials of the phases.We also identify the conditions at which a fluctuation may convert to a different phase as its size increases, referred to here as a "fluctuation phase transition" (FPT). We demonstrate these phenonena in simulations of a two dimensional lattice model by evaluating the free energy surface that describes the thermodynamic properties of a fluctuation as a function of its size and phase composition. We show that a FPT can occur in the fluctuations of either a stable or metastable bulk phase and that the transition is first-order. We also find that the FPT is bracketed by welldefined spinodals, which place limits on the size of fluctuations of distinct phases. Furthermore, when the FPT occurs in a metastable bulk phase, we show that the superposition of the FPT on the nucleation process results in two-step nucleation (TSN). We identify distinct regimes of TSN based on the nucleation pathway in the free energy surface, and correlate these regimes to the phase diagram of the bulk system. Our results clarify the origin of TSN, and elucidate a wide variety of phenomena associated with TSN, including the Ostwald step rule. arXiv:1809.01783v1 [cond-mat.stat-mech]

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Section: Relationship To Previous Modelling Of Two-step Nucle-ationcontrasting

confidence: 99%

Phase transitions in fluctuations and their role in two-step nucleation

James

Beairsto

Hartt

et al. 2019

The Journal of Chemical Physics

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“…A saddle point associated with a pure liquid critical cluster leads to the liquid free-energy basin, which is then separated from the △-crystal basin by a ridge on the free-energy surface, so nucleation requires the crossing of two barriers. Accounting for the disjoining pressure [37,38] associated with the thin wetting layer and the strain energy of the lattice [15], the CNT introduces a saddle point on the free-energy surface with a liquid-△-solid critical cluster leading directly to the crystal phase, as observed in our simulations, but the valley floor approaching this saddle point, and hence the precritical fluctuations, grows along the △-solid axis. In our simulation results, the early stages of nucleation are characterized by the formation of pure liquidlike clusters, which is at odds with CNT.…”

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confidence: 49%

Nonclassical Nucleation in a Solid-Solid Transition of Confined Hard Spheres

Peng

Han

et al. 2015

Phys. Rev. Lett.

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A solid-solid phase transition of colloidal hard spheres confined between two planar hard walls is studied using a combination of molecular dynamics and Monte Carlo simulation. The transition from a solid consisting of five crystalline layers with square symmetry (5□) to a solid consisting of four layers with triangular symmetry (4△) is shown to occur through a nonclassical nucleation mechanism that involves the initial formation of a precritical liquid cluster, within which the cluster of the stable 4△ phase grows. Free-energy calculations show that the transition occurs in one step, crossing a single free-energy barrier, and that the critical nucleus consists of a small 4△ solid cluster wetted by a metastable liquid. In addition, the liquid cluster and the solid cluster are shown to grow at the planar hard walls. We also find that the critical nucleus size increases with supersaturation, which is at odds with classical nucleation theory. The △-solid-like cluster is shown to contain both face-centered-cubic and hexagonal-close-packed ordered particles. The kinetics of phase transitions plays an important role in condensed-matter physics and materials science. In order to gain a better fundamental understanding of how to control self-assembly processes in the fabrication of novel structures, many experimental and simulation studies have been devoted to colloidal systems. Experiments [1-4] and computer simulations [5][6][7] on bulk hard-sphere colloids suggested that the metastable fluid crystallizes and superheated crystals melt via a single-step nucleation process that is well described by classical nucleation theory (CNT) [8]. However, Ostwald's step rule suggests that the kinetic pathway to the most stable state can initially proceed through the nucleation of intermediate, metastable phases [9]. The effect of a nearby metastable state on nucleation and the occurrence of multistep nucleation processes have been studied in the crystallization of a range of systems including colloids [10,11], proteins [12], and patchy particles [13], and in the crystallization of molecular solids from solution [14].In contrast, the kinetic processes of solid-solid phase transitions, which involve complex structural rearrangements [15], have received considerably less attention [16]. Solid-solid transitions usually occur in a martensitic fashion [17,18] involving the concerted, diffusionless motion of the atoms in the unit cell. Anisotropic stress, rapid quenching, and a small system size have been found to promote martensitic transformations [19]. In colloids, martensitic transitions have been observed in small crystalline clusters [20][21][22] or lattices stretched by external fields [18,[23][24][25]. A solid-solid transition involving an activated nucleation process has recently been experimentally observed at the single-particle level for the first time in colloidal thin-film crystals confined between two glass plates [26]. The equilibrium phase diagram of hard spheres confined between two planar hard walls shows an alternati...

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“…The model calculation [2] using the Monte Carlo simulation with a simpli¿ed intermolecular interaction revealed that the critical nucleus at the saddle point corresponds indeed to the core-shell composite structure. Subsequent Monte Carlo simulation using more realistic Lennard-Jones system [3] and a model calculation using the capillarity approximation [4] con¿rmed the core-shell structure of critical nucleus which corresponds to the saddle point of the free-energy landscape in the two-dimensional space of stable and metastable components. A similar core-shell composite nucleus is predicted even for a simple metal like aluminum using molecular dynamics simulation.…”

Section: Introductionmentioning

confidence: 89%

Characterizing the nucleation flux of linked-flux model for core-shell composite nucleus

Iwamatsu¹

2013

AIP Conference Proceedings

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The kinetics of nucleation of a core-shell composite nucleus that consists of a core of stable ¿nal phase surrounded by a wetting layer of an intermediate metastable phase is studied using the linked-Àux model where the nucleation Àux is considered in the two-dimensional space of stable and metastable components. The steady-state solution of the Fokker-Planck equation is considered not only in the size and composition space but also in the component space. It is shown that the kinetics of critical nucleus at the saddle point is more appropriately characterized in the size and composition space, while the kinetics of the post-critical nucleus is more appropriately described in the component space. Although both the free-energy landscape and the reaction rates play decisive role to determine the kinetics of nucleation at the saddle point, the details of the free energy landscape are irrelevant to the kinetics of the post critical nucleus.

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Free-energy landscape of nucleation with an intermediate metastable phase studied using capillarity approximation

Cited by 24 publications

References 45 publications

Phase transitions in fluctuations and their role in two-step nucleation

Phase transitions in fluctuations and their role in two-step nucleation

Nonclassical Nucleation in a Solid-Solid Transition of Confined Hard Spheres

Characterizing the nucleation flux of linked-flux model for core-shell composite nucleus

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