Identifying Vibrations That Destabilize Crystals and Characterize the Glassy State

Greaves, G.N.; Meneau, Florian; Majérus, Odile; Jones, D. G.; Taylor, Jonathan

doi:10.1126/science.1109411

Cited by 103 publications

(131 citation statements)

References 26 publications

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“…For instance, the comparison of densified silica glass and α-cristobalite . Although this opposite trend is rare, it was observed, e.g., for amorphous and crystalline zeolite [27,28].…”

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Role of Disorder in the Thermodynamics and Atomic Dynamics of Glasses

et al. 2014

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We measured the density of vibrational states (DOS) and the specific heat of various glassy and crystalline polymorphs of SiO 2 . The typical (ambient) glass shows a well-known excess of specific heat relative to the typical crystal (α-quartz). This, however, holds when comparing a lower-density glass to a higherdensity crystal. For glassy and crystalline polymorphs with matched densities, the DOS of the glass appears as the smoothed counterpart of the DOS of the corresponding crystal; it reveals the same number of the excess states relative to the Debye model, the same number of all states in the low-energy region, and it provides the same specific heat. This shows that glasses have higher specific heat than crystals not due to disorder, but because the typical glass has lower density than the typical crystal. DOI: 10.1103/PhysRevLett.112.025502 PACS numbers: 63.20.-e, 07.85.-m, 76.80.+y The low-temperature thermodynamic properties of glasses are accepted to be anomalously different from those of crystals due to the inherent disorder of the glass structure. At temperatures of ∼10 K, the specific heat of glasses shows an excess relativetothatofthecorrespondingcrystals.Theexcessspecific heat is related to a distinct feature in the spectrum of the atomic vibrations: At frequencies of ∼1 THz, glasses exhibit an excess of states above the Debye level of the acoustic waves, the socalled "boson peak." The excess of specific heat and the boson peak are universally observed for all glasses and by all relevant experimental techniques. However, the results still do not converge to a unified answer to how disorder causes these anomalies.Themajorityofthemodelsexplainthebosonpeakbyappealing tovarious glass-specific features. Theseincludelow-energy optical modes [1], onset of mechanical instability related to saddle points in the energy landscape [2] or to jamming [3][4][5], local vibrationalmodes of clusters [6] or locally favoured structures [7], librations [8] or other coherent motions [9] of molecular fragments, crossover of local and acoustic modes [10], quasilocal vibrations of atoms in an anharmonic potential [11], broadening of vibrational states in the Ioffe-Regel crossover regime [12], spatial variation of the elastic moduli [13], breakdown of the continuum approximation [14,15], and topologically diverse defects [16], to cite the most important ones.Alternatively, the boson peak is identified as the counterpart of the acoustic van Hove singularities of crystals, i.e., explained by the piling up of the vibrational states of the acousticlike branches near the boundary of the pseudoBrillouin zone [17][18][19][20].Diverging in explanations of the boson peak, all models agree that the excess states and the excess specific heat of

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“…For instance, the comparison of densified silica glass and α-cristobalite . Although this opposite trend is rare, it was observed, e.g., for amorphous and crystalline zeolite [27,28].…”

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confidence: 95%

“…A check of the densities of the various SiO 2 polymorphs (Table 1) [27,28]). A different density is accompanied by different sound velocity [29], which determines different properties of the elastic medium of the glass and influences its atomic dynamics [20,30,31].…”

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confidence: 99%

Role of Disorder in the Thermodynamics and Atomic Dynamics of Glasses

et al. 2014

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“…At the GT, because only 2D closed cycle-flow (that will generate a non-integrable phase  and an additional z-axial induced energy) corresponds to the abnormal heat capacity and boson peak [3,[7][8][9], we need only discuss all the IE loopflows on reference 0 (particle local) filed. The discussion further simplify to only consider the loop-flows formed by several consecutive arrows on a 2D projection plane, see Figures 2-5, and each arrow denotes an IE that has the same IE energy a   for flexible chain system.…”

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confidence: 99%

Universal 2D Soft Nano-Scale Mosaic Structure Theory for Polymers and Colloids

Wu¹

2011

SNL

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“…Importantly, recent studies revealed that ZIFs may experience pressure-or temperature-induced amorphization [18]. Amorphization phenomena are better understood in inorganic zeolites, where low-energy vibrations that resonate at terahertz (THz) frequencies could destabilize porous crystals, causing structural instability and collapse [19].…”

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Identifying the Role of Terahertz Vibrations in Metal-Organic Frameworks: From Gate-Opening Phenomenon to Shear-Driven Structural Destabilization

et al. 2014

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We present an unambiguous identification of low-frequency terahertz vibrations in the archetypal imidazole-based metal-organic framework (MOF) materials: ZIF-4, ZIF-7, and ZIF-8, all of which adopt a zeolite-like nanoporous structure. Using inelastic neutron scattering and synchrotron radiation far-infrared absorption spectroscopy, in conjunction with density functional theory (DFT), we have pinpointed all major sources of vibrational modes. Ab initio DFT calculations revealed the complex nature of the collective THz modes, which enable us to establish detailed correlations with experiments. We discover that low-energy conformational dynamics offers multiple pathways to elucidate novel physical phenomena observed in MOFs. New evidence demonstrates that THz modes are intrinsically linked, not only to anomalous elasticity underpinning gate-opening and pore-breathing mechanisms, but also to shear-induced phase transitions and the onset of structural instability.

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Identifying Vibrations That Destabilize Crystals and Characterize the Glassy State

Cited by 103 publications

References 26 publications

Role of Disorder in the Thermodynamics and Atomic Dynamics of Glasses

Role of Disorder in the Thermodynamics and Atomic Dynamics of Glasses

Universal 2D Soft Nano-Scale Mosaic Structure Theory for Polymers and Colloids

Identifying the Role of Terahertz Vibrations in Metal-Organic Frameworks: From Gate-Opening Phenomenon to Shear-Driven Structural Destabilization

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