Delocalization of the atom in glass and its liquids

Сандитов, Д. С.; Badmaev, S. S.

doi:10.1134/s1087659615050156

Cited by 13 publications

(7 citation statements)

References 13 publications

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“…valence bonds [7,8]. We believe that atom delocalization as an ultimate displacement of a bridging atom is a necessary condition for an elementary event in the process of viscous flow of inorganic glass (for example, valence bond switching [5]).…”

Section: Glass-liquid Transition As a Consequence Of Atom Delocalizationmentioning

confidence: 99%

“…In inorganic glasses, amorphous metallic alloys, amorphous organic polymers, and lowmolecular-weight organic glasses, the fraction of the fluctuation volume, fg, frozen at the glass transition temperature, Tg, weakly depends on the nature of the glass (Table 2) and ranges typically: Table 2. Parameters of the Williams-Landel-Ferry (WLF) equation (C1 and C2) and fraction of the fluctuation volume, fg, frozen at glass transition temperature, Tg [2,7,8,9]. WLF equation is as follows:…”

Section: Rd E = εmentioning

confidence: 99%

“…Tg, for the sodium silicate glasses (see Table 2). The value of fg can be determined from viscosity data in the glass transition region [7,8]. The fg of the sulfophosphate glasses also varies in a narrow range (fg ≈ const), but it is markedly smaller than that of the silicate glasses ( Table 1).…”

Section: Amorphous Substancementioning

confidence: 99%

“…As pointed out above, bridging "pivot" atoms, such as oxygen atom in a Si-O-Si bridge, act as kinetic units capable of delocalization in inorganic glasses. Because of this, the atom delocalization volume Δve in a given class of glasses is essentially constant: Δve ≈ const [2,7,8].…”

Section: Glass "Plasticity" and Atom Delocalizationmentioning

confidence: 99%

“…[1][2][3][4][5][6]. In this paper, using delocalized-atom model previously developed [2,7,8] we compare glass softening with reversible frozen deformation of glassy solids, which makes it possible to gain certain information about glass-liquid transition and vitrification processes. In addition, we discuss a possible scenario of liquid-glass transition based on switching off the creep triggering mechanism: atom delocalization.…”

Section: Introductionmentioning

confidence: 99%

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Glass transition criterion and plastic deformation of glass

Сандитов

Ojovan

Darmaev

2020

Physica B: Condensed Matter

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We develop the notion that amorphous substances undergo reversible configurational structural changes accompanied by local expansion and compression (atom delocalization) near the glass transition temperature. They are similar in nature to configurational changes in the structure of glasses in the case of reversible frozen (plastic) deformation and its thermally stimulated relaxation. We assume that the glass-liquid transition is associated with the process of atom delocalization caused by bond breaking and formation of elementary excitations e.g. configurons. We discuss the possibility of detection of configuron formation and atom delocalization near glass transition based on temperature dependence of X-rays or neutron first sharp diffraction (pair distribution function) minimum.

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Section: Glass-liquid Transition As a Consequence Of Atom Delocalizationmentioning

confidence: 99%

Section: Rd E = εmentioning

confidence: 99%

Section: Amorphous Substancementioning

confidence: 99%

Section: Glass "Plasticity" and Atom Delocalizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Glass transition criterion and plastic deformation of glass

Сандитов

Ojovan

Darmaev

2020

Physica B: Condensed Matter

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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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Delocalized-Atom Model and Properties of Sulfophosphate Glasses

Сандитов

Badmaev

2019

Inorg Mater

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Delocalization of the atom in glass and its liquids

Cited by 13 publications

References 13 publications

Glass transition criterion and plastic deformation of glass

Glass transition criterion and plastic deformation of glass

On relaxation nature of glass transition in amorphous materials

Delocalized-Atom Model and Properties of Sulfophosphate Glasses

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