Spectrum of relaxation times in GeO2 glass

Napolitano, Albert; Macedo, P. B.

doi:10.6028/jres.072a.034

Cited by 53 publications

(19 citation statements)

References 13 publications

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“…4 (data from refs. [22][23][24]. It shows fits to the dielectric relaxation time scale of 3-bromopentane (3BP) and viscosity of ortho-terphenyl (OTP), by using fϭ0 , and an Arrhenius fit to the viscosity data of GeO 2 , by using fϭ1 .…”

Section: Comparison With Experimentsmentioning

confidence: 99%

Coarse-grained microscopic model of glass formers

Garrahan

Chandler

2003

Proc. Natl. Acad. Sci. U.S.A.

305

315

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We introduce a coarse-grained model for atomic glass formers. Its elements are physically motivated local microscopic dynamical rules parameterized by observables. Results of the model are established and used to interpret the measured behaviors of supercooled fluids approaching glass transitions. The model predicts the presence of a crossover from hierarchical super-Arrhenius dynamics at short length scales to diffusive Arrhenius dynamics at large length scales. This prediction distinguishes our model from other theories of glass formers and can be tested by experiment.I n this article, we introduce a microscopic model of glassforming supercooled liquids. It is a coarse-grained model with local dynamical rules, the elements of which can be measured. The rules contain only the physical features of detailed balance, dynamic facilitation, and persistence of particle-flow direction. Our analysis of the model indicates that these features are all that is required to explain the time-dependent and thermal behaviors of supercooled glass-forming liquids. For such systems, relaxation times grow rapidly with decreasing temperature T, usually more rapidly than exponentially in T Ϫ1 . This non-Arrhenius (or super-Arrhenius) temperature dependence often coincides with a relatively large change in heat capacity at the glass transition. On the other hand, liquids with relaxation times that grow in an Arrhenius fashion with decreasing temperature often display small changes in heat capacity at the glass transition. Apparent correlations such as these between thermodynamic properties and relaxation times have led to a commonly held opinion that a finite-temperature thermodynamic transition somehow underlies a glass transition (for a review of this and other views, see refs. 1 and 2). In contrast, our model explains the empirically observed correlations of relaxation and calorimetric properties at the glass transition without recourse to unusual or precipitous thermodynamics.Our model is described in terms of a grid or lattice in space-time. Underlying this discrete picture are certain ideas about continuous atomic motions in a supercooled liquid. The first idea is that particle mobility is sparse. Most atomic motions are small-amplitude vibrations and not diffusion steps. Most molecules are effectively jammed. The second idea is that particle mobility in a glass former is the result of facilitation (3-5). Specifically, a region of jammed atoms can become unjammed and thus exhibit mobility only when it is adjacent to a region that is already unjammed. This idea implies that mobile or unjammed particles form chains in space-time. Chains of mobile particles have been revealed by atomistic computer simulations of supercooled liquids (6, 7). The third idea is that mobility carries a direction, and it is possible for this direction to persist in a glass former for significant periods of time. This convective-like quality of particle motion is also revealed by the atomistic computer simulations of supercooled liquids (6, 7).To help il...

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Section: Comparison With Experimentsmentioning

confidence: 99%

Coarse-grained microscopic model of glass formers

Garrahan

Chandler

2003

Proc. Natl. Acad. Sci. U.S.A.

305

315

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“…Macroscopic quantities like viscosity, refractive index, volume or elastic constants, are usually the subject of this kind of studies. [3][4][5][6][7][8][9][10] In these works, the investigated quantities evolve with waiting time, t w , in a way which depends on the previous thermal history and which can be accurately described by stretched exponential functions. 6 Similar results have been reported also in studies of aging effect on the intensity of the high frequency tail of the dielectric spectra.…”

Section: Introductionmentioning

confidence: 99%

Compressed correlation functions and fast aging dynamics in metallic glasses

Ruta

Baldi²,

Monaco

et al. 2013

The Journal of Chemical Physics

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We present x-ray photon correlation spectroscopy measurements of the atomic dynamics in a Zr 67 Ni 33 metallic glass, well below its glass transition temperature. We find that the decay of the density fluctuations can be well described by compressed, thus faster than exponential, correlation functions which can be modeled by the well-known Kohlrausch-Williams-Watts function with a shape exponent β larger than one. This parameter is furthermore found to be independent of both waiting time and wave-vector, leading to the possibility to rescale all the correlation functions to a single master curve. The dynamics in the glassy state is additionally characterized by different aging regimes which persist in the deep glassy state. These features seem to be universal in metallic glasses and suggest a nondiffusive nature of the dynamics. This universality is supported by the possibility of describing the fast increase of the structural relaxation time with waiting time using a unique model function, independently of the microscopic details of the system.

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“…The volume first increased to a certain value and then decreased towards the equilibrium value. The phenomenon has been studied by measuring the refractive index of a borosilicate glass [11,15] and of GeO 2 glass [17], by measuring the volume by dilatometry and the rate of enthalpy release of poly(styrene) by adiabatic microcalorimetry [19,20,26]. It has been investigated also by dielectric [28] and dynamics mechanical measurements [27].…”

Section: Results and Analysismentioning

confidence: 99%

“…Its few studies have been limited mostly to polymers by measuring the volume [11,12,19,20,23,24,29,37,38], enthalpy [19,24,26,48], dielectric [28] and dynamic mechanical relaxation [27], creep [29], and combined creep compliance and volume [31,32]. It has been studied by refractive index measurements [11,15,17] and, in a remarkable investigation, by creep-compliance and volume measurements of an epoxy polymer by changing the water content instead of the temperature [49]. It should be mentioned that Illers [50] had reported appearance of an endothermic peak at T < T g in his differential scanning calorimetry (DSC) heating scan of annealed partially crystalline poly(vinyl chloride).…”

Section: Introductionmentioning

confidence: 99%