Nonergodicity Factor, Fragility, and Elastic Properties of Polymeric Glassy Sulfur

Abstract

We present a detailed investigation of the vibrational dynamics of glassy sulfur (g-S). The large frequency range spanned in this study has allowed us to carefully scrutinize the elastic properties of g-S and to analyze their relation to various features of both the glassy and the liquid state. In particular, the acoustic properties of g-S present a quasi-harmonic behavior in the THz frequency range, while at lower frequency, in the GHz range, they are affected by a strong anharmonic contribution. Moreover, the high frequency (THz) dynamics of g-S does not present signatures of the elastic anomalies recently observed in a number of glasses. Despite this apparent contradiction, we show that this finding is not in disagreement with the previous ones. Finally, by considering the correct long wavelength limit of the density fluctuations in the glassy state, we estimate the continuum limit of the nonergodicity factor and we investigate recently proposed relations between the fast dynamics of glasses and the slow dynamics of the corresponding viscous melts.

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

“…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).…”

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

“…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.…”

Free-volume dependent atomic dynamics in beta relaxation pronounced La-based metallic glasses

“…q is the product between the contrast and the nonergodicity factor [24], s the structural relaxation time and n the shape parameter. With increasing temperature the dynamics shifts toward faster time scales due to the thermal effect, but at 363 K an anomalous slowing down of the dynamics is observed.…”