Model of delocalized atoms in the physics of the vitreous state

Сандитов, Д. С.

doi:10.1134/s1063776112060143

Cited by 49 publications

(34 citation statements)

References 25 publications

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“…If we assume that the increment of the volume ΔV/V in relation (16) also results from the delocalization of atoms under a mechanical effect, a definite interrelation between (1 -2μ) and the fluctuation volume of atom delocal ization Δv e = πd 2 Δr m can be expected; this fluctuation volume is calculated as follows [8] (Table 3):…”

Section: Discussionmentioning

confidence: 99%

“…It is easy to verify that, for the thermal expansion coefficient of the fluctuation volume Eq. (7) yields the following relation: using dependence (7) for (ΔH e /kT), we obtain the fol lowing formula from the above relation: (8) Here, the close orders of magnitudes of the volumes Δv e and v are allowed for.…”

Section: Gruneisen Parameter and Fluctuation Volumementioning

confidence: 99%

“…A kinetic unit (an atom or a group of atoms) that undergoes critical displacement is called a delocalized atom; the approach itself, the model of delocalized atoms [8]. (1) Equation (1) implies that volume variations lead to a relative change in the frequency that is the same for all oscillation modes.…”

Section: Introductionmentioning

confidence: 99%

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Gruneisen parameter and fluctuation volume of amorphous polymers and glass

2013

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Section: Discussionmentioning

confidence: 99%

Section: Gruneisen Parameter and Fluctuation Volumementioning

confidence: 99%

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Gruneisen parameter and fluctuation volume of amorphous polymers and glass

2013

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“…(2) within the relaxation theory of glass transition [8], with the use of the model of delocalized atoms [9].…”

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confidence: 99%

“…The delocalization of an atom or, in other words, the excitation of an atom [13] assumes its fluctuation critical shift Δr m from equilibrium, which corresponds to the inflection point of the curve of potential U(r), in other words, the max imum atomic attraction (see figure) [9]. One of the important parameters of model is the fluctuation vol ume of amorphous medium ΔV e that appears after the delocalization of the atoms…”

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confidence: 99%

Criterion of vitrification and cooling rate of vitreous melts

2014

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Based on the equation for the dependence of the glass transition temperature vs. the cooling rate, the analogous dependence has been determined for the fraction of fluctuation volume, which is frozen at the glass transition temperature. It has been shown that the constant ratio of empirical constants of the given equation is the consequence of the criterion of vitrification in the model of delocalized atoms. The nature of the free volume of amorphous substances has been discussed.

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On relaxation nature of glass transition in amorphous materials

Сандитов

Ojovan

2017

Physica B: Condensed Matter

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A short review on relaxation theories of glass transition is presented. The main attention is paid to modern aspects of the glass transition equation qτg = C, suggested by Bartenev in 1951 (q – cooling rate of the melt, τg – structural relaxation time at the glass transition temperature Tg). This equation represents a criterion of structural relaxation at transition from liquid to glass at T = Tg (analogous to the condition of mechanical relaxation ωτ = 1, where the maximum of mechanical loss is observed). The empirical parameter С = δTg has the meaning of temperature range δTg that characterizes the liquid-glass transition. Different approaches of δTg calculation are reviewed. In the framework of the model of delocalized atoms a modified kinetic criterion of glass transition is proposed (q/Tg)τg = Cg, where Cg ≅ 7·10−3 is a practically universal dimensionless constant. It depends on fraction of fluctuation volume fg, which is frozen at the glass transition temperature Cg = fg/ln(1/fg). The value of fg is approximately constant fg ≅ 0.025. At Tg 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 flow – activated 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 Tg, 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 Tg = Tg(q) is discussed. The value of fg calculated from the data on the Tg(q) dependence coincides with result of the fg 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 Tg(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

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Model of delocalized atoms in the physics of the vitreous state

Cited by 49 publications

References 25 publications

Gruneisen parameter and fluctuation volume of amorphous polymers and glass

Gruneisen parameter and fluctuation volume of amorphous polymers and glass

Criterion of vitrification and cooling rate of vitreous melts

On relaxation nature of glass transition in amorphous materials

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