The role of local structure in dynamical arrest

Royall, C. Patrick; Williams, Stephen R.

doi:10.1016/j.physrep.2014.11.004

Cited by 406 publications

(483 citation statements)

References 564 publications

(1,149 reference statements)

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“…18 At higher temperatures, there is an increase in both the atomic displacements and the number of atoms participating in the jumps. 21 It is pertinent to note that, although crystallisation is universally known to be a first-order thermodynamic transformation, 22,23 glass transition has been prevailingly considered as a largely dynamical phenomenon 24 and soft phonons are known to be related to the dynamics of amorphous alloys. 18,25 Although the energy landscape curvature and mean-squared atomic displacements (MSD) are two different quantities, they are inter-connected often in complicated relations.…”

Section: Resultsmentioning

confidence: 99%

Softening of phonon spectra in metallic glasses

et al. 2016

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The vibrational spectra of a series of MgZnCa amorphous alloys were computed using density functional theory and implementing the small displacement method. The atomic structures of the alloys were obtained by ab initio molecular dynamics simulations. The vibrational thermodynamic properties were calculated as a function of temperature and, in particular, the specific heat at low temperature was approximated by temperature cubed based on the Debye model. We computed the contribution of Mg vibrations to the specific heat and investigated the softening of Mg phonon spectra, where the maximum allowed vibrational frequency is lowered and highly collective diffusion processes are promoted. The statistical correlation between the reported critical casting thickness of the alloys and softening of Mg phonons was obtained. Similar calculations were performed for two distinctively different amorphous ZrTiCuAl alloys with large and small reported critical casting thickness, respectively. The findings were consistent with those of the MgZnCa alloys. INTRODUCTIONThere has been increasing attention devoted to the effect of vibrational thermodynamics on the formation of different alloy phases and their associated phase transformations due to the improved accessibility of instruments capable of measuring and calculating the phonon frequencies. 1 Various thermodynamic properties such as specific heat and vibrational entropy can be derived through the vibrational density of states (VDOSs). The VDOS obtained by molecular dynamics (MD) simulations has provided useful insight into how phonon spectra are affected by both the size and surface properties of silicon nanoparticles; this is of major significance in the design of nanodevices with better heat transport properties. It was found that, as the Si particles become smaller, the density of vibrational states increases at low frequencies, and modes are transferred from the high-frequency end to the intermediate range and transverse optical modes peak are shifted to higher frequencies. 2 In metallic glasses, vibrational characteristics have also been used for explaining mechanical properties. For example, recent MD simulations of a Cu 64 Zr 36 metallic glass showed that the strongest participation in the modes with lowest vibrational frequency and, hence, weakest spring constants (i.e., soft modes) originate predominantly from meagrely populated polyhedra. These soft spots provide fertile sites for accommodating shear transformations. 3 The softening of long wavelength acoustic phonons in PdSiCu, ZrTiCuNiBe, CeAlNiCu and ZrNbCuNiBe amorphous alloys relative to their crystalline phases have been observed experimentally using ultrasound measurements. [4][5][6] Such observations are consistent with the low-temperature measurements of their specific heat, whereby an increase in temperature causes a steeper increase in specific heat in the amorphous alloys compared with their crystalline counterparts.Specific heat is believed to be a fundamental property of materials and, in particular,...

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Section: Resultsmentioning

confidence: 99%

Softening of phonon spectra in metallic glasses

et al. 2016

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“…Several studies have shown instead that the supercooled state contains a lot of structural order aside from crystalline order [34,35]. For hard spheres, for example, the competition between crystalline order and icosahedral (or five-fold symmetric) order plays a big role in the nucleation process, and on its avoidance [12,17,18,44,[54][55][56][57]. For systems with a metastable critical point, e.g.…”

Section: Extending Classical Nucleation Theorymentioning

confidence: 99%

Crystal nucleation as the ordering of multiple order parameters

Russo

Tanaka

2016

The Journal of Chemical Physics

107

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Nucleation is an activated process in which the system has to overcome a free energy barrier in order for a first-order phase transition between the metastable and the stable phases to take place. In the liquid-to-solid transition the process occurs between phases of different symmetry, and it is thus inherently a multi-dimensional process, in which all symmetries are broken at the transition. In this Focus Article, we consider some recent studies which highlight the multi-dimensional nature of the nucleation process. Even for a single-component system, the formation of solid crystals from the metastable melt involves fluctuations of two (or more) order parameters, often associated with the decoupling of positional and orientational symmetry breaking. In other words, we need at least two order parameters to describe the free-energy of a system including its liquid and crystalline states. This decoupling occurs naturally for asymmetric particles or directional interactions, focusing here on the case of water, but we will show that it also affects spherically symmetric interacting particles, such as the hard-sphere system. We will show how the treatment of nucleation as a multi-dimensional process has shed new light on the process of polymorph selection, on the effect of external fields on the nucleation process, and on glass-forming ability.

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“…There is a long tradition in the theory of glasses of attributing glass behavior to the growth of particular types of structural order, such as icosahedral order in three dimensions [17][18][19]. Recent work by Cubuk et al [20] on the flow of jammed and glassy systems under stress has shown that regions that are susceptible to rearrangement can be discovered by machine-learning methods that combine information derived from several features of the local structure, such as the radial distribution of particles and the bond angles.…”

Section: Introductionmentioning

confidence: 99%

Understanding the ideal glass transition: Lessons from an equilibrium study of hard disks in a channel

Godfrey

Moore

2015

Phys. Rev. E

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We use an exact transfer-matrix approach to compute the equilibrium properties of a system of hard disks of diameter σ confined to a two-dimensional channel of width 1.95 σ at constant longitudinal applied force. At this channel width, which is sufficient for next-nearest-neighbor disks to interact, the system is known to have a great many jammed states. Our calculations show that the longitudinal force (pressure) extrapolates to infinity at a well-defined packing fraction φK that is less than the maximum possible φmax, the latter corresponding to a buckled crystal. In this quasi-onedimensional problem there is no question of there being any real divergence of the pressure at φK . We give arguments that this avoided phase transition is a structural feature -the remnant in our narrow channel system of the hexatic to crystal transition -but that it has the phenomenology of the (avoided) ideal glass transition. We identify a length scaleξ3 as our equivalent of the penetration length for amorphous order: In the channel system, it reaches a maximum value of around 15 σ at φK , which is larger than the penetration lengths that have been reported for three dimensional systems. It is argued that the α-relaxation time would appear on extrapolation to diverge in a Vogel-Fulcher manner as the packing fraction approaches φK .

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The role of local structure in dynamical arrest

Cited by 406 publications

References 564 publications

Softening of phonon spectra in metallic glasses

Softening of phonon spectra in metallic glasses

Crystal nucleation as the ordering of multiple order parameters

Understanding the ideal glass transition: Lessons from an equilibrium study of hard disks in a channel

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