In Situ High-Temperature Probing of the Local Order of a Silicate Glass and Melt during Structural Relaxation (original) (raw)

Structural Relaxation Dynamics and Annealing Effects of Sodium Silicate Glass

The Journal of Physical Chemistry B, 2013

Here we report high-precision measurements of structural relaxation dynamics in the glass transition range at the intermediate and short length scale for a strong sodium silicate glass during long annealing times. We evidence for the first time the heterogeneous dynamics at the intermediate range order by probing the acoustic longitudinal frequency in the GHz region by Brillouin light scattering spectroscopy. Or, from in−situ Raman measurements, we show that relaxation is indeed homogeneous at the interatomic length scale. Our results show that the dynamics at the intermediate range order contains two distinct relaxation time scales, a fast and a slow component, differing by about a 10-fold factor below T g and approaching to one another past the glass transition. The slow relaxation time agrees with the shear relaxation time, proving that Si−O bond breaking constitutes the primary control of structural relaxation at the intermediate range order.

Structure and properties of densified silica glass: characterizing the order within disorder

NPG Asia Materials

The broken symmetry in the atomic-scale ordering of glassy versus crystalline solids leads to a daunting challenge to provide suitable metrics for describing the order within disorder, especially on length scales beyond the nearest neighbor that are characterized by rich structural complexity. Here, we address this challenge for silica, a canonical network-forming glass, by using hot versus cold compression to (i) systematically increase the structural ordering after densification and (ii) prepare two glasses with the same high-density but contrasting structures. The structure was measured by high-energy X-ray and neutron diffraction, and atomistic models were generated that reproduce the experimental results. The vibrational and thermodynamic properties of the glasses were probed by using inelastic neutron scattering and calorimetry, respectively. Traditional measures of amorphous structures show relatively subtle changes upon compacting the glass. The method of persistent homology...

Relaxation dynamics of glasses along a wide stability and temperature range

Scientific Reports, 2016

While lots of measurements describe the relaxation dynamics of the liquid state, experimental data of the glass dynamics at high temperatures are much scarcer. We use ultrafast scanning calorimetry to expand the timescales of the glass to much shorter values than previously achieved. Our data show that the relaxation time of glasses follows a super-Arrhenius behaviour in the high-temperature regime above the conventional devitrification temperature heating at 10 K/min. The liquid and glass states can be described by a common VFT-like expression that solely depends on temperature and limiting fictive temperature. We apply this common description to nearly-isotropic glasses of indomethacin, toluene and to recent data on metallic glasses. We also show that the dynamics of indomethacin glasses obey density scaling laws originally derived for the liquid. This work provides a strong connection between the dynamics of the equilibrium supercooled liquid and non-equilibrium glassy states.

Link between Medium and Long-range Order and Macroscopic Properties of Silicate Glasses and Melts

Reviews in Mineralogy and Geochemistry

Understanding the cationic network and the medium range order of glasses and melts allows rationalization of each elements role in terms of the network former, charge compensator or network modifier concepts. Such knowledge can be combined with further details, e.g. regarding the role of highly coordinated network former elements, to model the macroscopic properties of glasses and melts, like their molar volume, density, configurational entropy and viscosity. In this chapter, we present recent advances on such work, which open new avenues for the production of useful and precise models of geologic and industrial glasses and melts.

On Structural Rearrangements Near the Glass Transition Temperature in Amorphous Silica

Materials

The formation of clusters was analyzed in a topologically disordered network of bonds of amorphous silica (SiO2) based on the Angell model of broken bonds termed configurons. It was shown that a fractal-dimensional configuron phase was formed in the amorphous silica above the glass transition temperature Tg. The glass transition was described in terms of the concepts of configuron percolation theory (CPT) using the Kantor-Webman theorem, which states that the rigidity threshold of an elastic percolating network is identical to the percolation threshold. The account of configuron phase formation above Tg showed that (i) the glass transition was similar in nature to the second-order phase transformations within the Ehrenfest classification and that (ii) although being reversible, it occurred differently when heating through the glass–liquid transition to that when cooling down in the liquid phase via vitrification. In contrast to typical second-order transformations, such as the forma...

The Structure of Silicate Glasses and Melts

Glasses and melts have unique physical and chemical properties, which vary as a function of temperature, pressure, and chemical composition. Understanding these properties requires an accurate structural description. The amorphous nature and complex chemical composition of glasses and melts do not allow the construction of a unique, crystal-like structural model. Nevertheless, despite the lack of periodicity and long-range order, glasses and melts retain a characteristic short-range order, which obeys basic crystal-chemical rules. However, only a limited amount of information exists about changes in a glass structure with temperature or pressure or both. Obtaining this information requires a combination of experimental and theoretical approaches. The connections between structural observations and melt properties are less well known, even at the qualitative level, although progress has been and continues to be made. Melt structure, properties, and dynamics were reviewed a decade ago and are discussed in detail in a recent book (Mysen and Richet 2005); we provide here only a few examples.

Direct evidence of rigidity loss and self-organisation in silicate glasses

2004

The Brillouin elastic free energy change DFDFDF between thermally annealed and quenched (Na2O)x(SiO2)1−x(Na_2O)_x(SiO_2)_{1-x}(Na2O)x(SiO2)1−x glasses is found to decrease linearly at x>0.23x > 0.23x>0.23 (floppy phase), and to nearly vanish at x<0.18x < 0.18x<0.18 (stressed- rigid phase). The observed DF(x)D F(x)DF(x) variation closely parallels the mean-field floppy mode fraction f(x)f(x)f(x) in random networks, and fixes the two (floppy, stressed-rigid) elastic phases. In calorimetric measurements, the non-reversing enthalpy near TgT_gTg is found to be large at x<0.18x < 0.18x<0.18 and at x>0.23x > 0.23x>0.23, but to nearly vanish in the 0.18<x<0.230.18 < x < 0.230.18<x<0.23 range, suggesting existence of an intermediate phase between the floppy and stressed-rigid phases.

Relaxation dynamics and aging in structural glasses

2013

We present a study of the atomic dynamics in a Mg 65 Cu 25 Y 10 metallic glass former both in the deep glassy state and in the supercooled liquid phase. Our results show that the glass transition is accompanied by a dynamical crossover between a faster than exponential shape of the intermediate scattering function in the glassy state and a slower than exponential shape in the supercooled liquid. While the crossover temperature is independent on the previous thermal history, both the relaxation rate and the shape of the relaxation process depend on the followed thermal path. Moreover, the temperature dependence of the the structural relaxation time displays a strong departure from the Arrhenius-like behavior of the corresponding supercooled liquid phase, and can be well described in the Narayanaswamy-Moynihan framework with a large non-linearity parameter.

On relaxation nature of glass transition in amorphous materials

Physica B-condensed Matter, 2017

A short review on relaxation theories of glass transition is presented. The main attention is paid to modern aspects of the glass transition equation qτ g = C, suggested by Bartenev in 1951 (qcooling rate of the melt, τ gstructural relaxation time at the glass transition temperature T g). This equation represents a criterion of structural relaxation at transition from liquid to glass at T = T g (analogous to the condition of mechanical relaxation ωτ = 1, where the maximum of mechanical loss is observed). The empirical parameter С = δT g has the meaning of temperature range δT g that characterizes the liquid-glass transition. Different approaches of δT g calculation are reviewed. In the framework of the model of delocalized atoms a modified kinetic criterion of glass transition is proposed (q/T g)τ g = C g , where C g ≅ 7•10 −3 is a practically universal dimensionless constant. It depends on fraction of fluctuation volume f g , which is frozen at the glass transition temperature C g = f g /ln(1/f g). The value of f g is approximately constant f g ≅ 0.025. At T g the process of atom delocalization, i.e. its displacement from the equilibrium position, is frozen. In silicate glasses atom delocalization is reduced to critical displacement of bridge oxygen atom in Si-O-Si bridge necessary to switch a valence bond according to Muller and Nemilov. An equation is derived for the temperature dependence of viscosity of glass-forming liquids in the wide temperature range, including the liquid-glass transition and the region of higher temperatures. Notion of (bridge) atom delocalization is developed, which is related to necessity of local low activation deformation of structural network for realization of elementary act of viscous flowactivated switch of a valence (bridge) bond. Without atom delocalization ("trigger mechanism") a switch of the valence bond is impossible and, consequently, the viscous flow. Thus the freezing of atom delocalization process at low temperatures, around T g , leads to the cease of the viscous flow and transition of a melt to a glassy state. This occurs when the energy of disordered lattice thermal vibrations averaged to one atom becomes equal or less than the energy of atom delocalization. The Bartenev equation for cooling rate dependence of glass transition temperature T g = T g (q) is discussed. The value of f g calculated from the data on the T g (q) dependence coincides with result of the f g calculation using the data on viscosity near the glass transition. Derivation of the Bartenev equation with the account of temperature dependence of activation energy of glass transition process is considered. The obtained generalized relation describes the T g (q) dependence in a wider interval of the cooling rate compared Bartenev equation. Experimental data related to standard cooling rate q = 3 K/min were used in this work.