Acoustic excitations in glassy sorbitol and their relation with the fragility and the boson peak

Ruta, Beatrice; Baldi, G.; Scarponi, F.; Fioretto, D.; Giordano, Valentina M.; Monaco, G.

doi:10.1063/1.4768955

Cited by 51 publications

(62 citation statements)

References 62 publications

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“…The f(q,t) corresponds to the dynamic structure factor normalized to the S(q) and gives therefore information on the dynamics on a spatial length scale defined by 2π/q. In glass formers, f(q,t) is usually described by the empirical Kohlrausch-Williams-Watt (KWW) function f(q,t)=fqexp(-t/τ) β [25], where τ is the characteristic relaxation time, β the shape parameter, and fq is the nonergodicity plateau before the final decay associated to structural relaxation [29,30]. In order to compare dynamic and structural properties, we performed two ramps in temperature, first heating the as-quenched sample up to 420 K (ramp 1) and then cooling it down again, always with a fixed rate of 1 K/min (ramp 2).…”

Section: Resultsmentioning

confidence: 99%

Structural and dynamical properties of Mg65Cu25Y10 metallic glasses studied by in situ high energy X-ray diffraction and time resolved X-ray photon correlation spectroscopy

Ruta

Giordano

Erra

et al. 2014

Journal of Alloys and Compounds

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We present a temperature investigation of the structural and dynamical evolution of rapidly quenched metallic glasses of Mg65Cu25Y10 at the atomic length scale by means of in situ high energy x-ray diffraction and time resolved x-ray photon correlation spectroscopy. We find a flattening of the temperature evolution of the position of the first sharp diffraction peak on approaching the glass transition temperature from the glassy state, which reflects into a surprising slowing down of the relaxation dynamics of even one order of magnitude with increasing temperature. The comparison between structural and dynamical properties strengthens the idea of a stress-induced, rather than pure diffusive, atomic motion in metallic glasses.

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Section: Resultsmentioning

confidence: 99%

Structural and dynamical properties of Mg65Cu25Y10 metallic glasses studied by in situ high energy X-ray diffraction and time resolved X-ray photon correlation spectroscopy

Ruta

Giordano

Erra

et al. 2014

Journal of Alloys and Compounds

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“…Another possibility is the use of the first moment sum rule, which, however, is helpful only if the temperature is sufficiently low that the intensities of the Stokes and anti-Stokes peaks differ significantly [27]. In principle, a good way to normalize the spectra also at high temperatures is given by the classical second moment sum rule [22,[28][29][30], but the use of this normalization procedure on the experimental data is of difficult implementation for two main reasons. One relates to the fact that the spectrum is the convolution of the dynamic structure factor with the resolution function, which has Lorentzian-like tails and thus its second moment is, strictly speaking, undefined.…”

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confidence: 99%

On the nontrivial wave-vector dependence of the elastic modulus of glasses

et al. 2016

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Recent theoretical models for the vibrations in glasses assume that the complex elastic modulus depends on frequency but not on the wave vector, q. This assumption translates in a simple q dependence of the dynamic structure factor, which can be experimentally tested. Following the suggestion of a recent paper [U. Buchenau, Phys. Rev. E 90, 062319 (2014)], we present here a new analysis, performed in q space, of inelastic x-ray scattering data of supercooled silica. The outcome of the analysis is compared to the more common approach in the frequency domain and indicates that the mentioned theoretical assumption is consistent with the data only below the boson peak frequency. At higher frequencies it gives rise to a breakdown of the classical second moment sum rule. This violation arises from the underlying assumption of the presence of a single excitation in the spectra. A comparison with the vibrational dynamics of α-cristobalite suggests, on the contrary, that in the terahertz frequency domain the inelastic spectrum of the glass gains contributions from both acousticlike and opticlike modes. A microscopic theory of the vibrations in glasses cannot neglect the medium range order in their structure, which gives rise to dispersion curves within a pseudo-Brillouin zone.

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“…The IXS cross section is proportional to the dynamic structure factor SðQ; ωÞ convoluted with the instrumental resolution function RðωÞ. The proportionality factor, which is a function of the analyzer reflectivity, the detectors efficiency, and the atomic form factors, is determined using the second moment sum rule [48]. At sufficiently low Q's the SðQ; ωÞ of a glass can be modeled as a delta function for the elastic line and a damped harmonic oscillator (DHO) for the inelastic component.…”

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Anharmonic Damping of Terahertz Acoustic Waves in a Network Glass and Its Effect on the Density of Vibrational States

Baldi¹,

Giordano

Ruta

et al. 2014

Phys. Rev. Lett.

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We report the observation, by means of high-resolution inelastic x-ray scattering, of an unusually large temperature dependence of the sound attenuation of a network glass at terahertz frequency, an unprecedentedly observed phenomenon. The anharmonicity can be ascribed to the interaction between the propagating acoustic wave and the bath of thermal vibrations. At low temperatures the sound attenuation follows a Rayleigh-Gans scattering law. As the temperature is increased the anharmonic process sets in, resulting in an almost quadratic frequency dependence of the damping in the entire frequency range. We show that the temperature variation of the sound damping accounts quantitatively for the temperature dependence of the density of vibrational states. DOI: 10.1103/PhysRevLett.112.125502 PACS numbers: 63.50.Lm, 62.30.+d, 62.65.+k, 66.70.Hk When the wavelength of a sound wave is sufficiently large with respect to the average size of the elastic modulus fluctuations, an amorphous solid behaves in a way similar to a continuous elastic medium. Since the elasticity of a glass is typically correlated on the nanometer scale [1][2][3], the wave propagation is influenced by the heterogeneous elasticity of the material when the frequency reaches the terahertz range [3]. A proper understanding of the propagation of elastic waves in random media is of great interest for many diverse fields. Examples are the attenuation of seismic waves in Earth's lithosphere [4,5] or the ability to tune the thermal conductivity of a thermoelectric material [6,7]. From a more fundamental perspective, the main unsolved problem concerns the nature of the vibrational modes of glasses in the few terahertz frequency range and the associated thermal transport properties [8][9][10]. The reduced density of vibrational states (RDOS) gðωÞ=ω 2 deviates from the Debye prediction and presents a peak, usually termed the boson peak (BP). This excess of states is often related to the known low temperature anomalies of the specific heat and of the thermal conductivity [8].Various models have been proposed to explain the BP anomaly, models that we can classify in three main groups, without the claim of being exhaustive. A first group includes those models, such as the soft potential model [11,12] and the jamming scenario [13], that associate the BP to quasilocalized soft modes. A second class of models relates the excess of states to the elastic heterogeneities of the glass. For instance, Ref. [14] suggests the appearance of localized modes close to the elastic heterogeneities, while the model of Refs. [15,16], recently extended to also take into account the role of anharmonic interactions [17], demonstrates that a distribution of random elastic constants can give rise to a peak in the RDOS. As a third class we mention those models where the BP is explained as a broadened first van Hove singularity, shifted to lower frequency by the disorder [18] and by the difference in mass density between the glass and the corresponding crystalline structure [19,20].The...

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Acoustic excitations in glassy sorbitol and their relation with the fragility and the boson peak

Cited by 51 publications

References 62 publications

Structural and dynamical properties of Mg65Cu25Y10 metallic glasses studied by in situ high energy X-ray diffraction and time resolved X-ray photon correlation spectroscopy

Structural and dynamical properties of Mg65Cu25Y10 metallic glasses studied by in situ high energy X-ray diffraction and time resolved X-ray photon correlation spectroscopy

On the nontrivial wave-vector dependence of the elastic modulus of glasses

Anharmonic Damping of Terahertz Acoustic Waves in a Network Glass and Its Effect on the Density of Vibrational States

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