Fragility and anharmonicity of lattice vibrations of glass-forming systems

Сандитов, Д. С.; Машанов, А. А.; Сандитов, Б. Д.; Mantatov, V. V.

doi:10.1134/s108765960804007x

Cited by 11 publications

(4 citation statements)

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“…Figure 5 further tests the m - ν correlation by including literature data on various oxide glass formers (Figure 5a) and all types of glass families (Figure 5b). The oxide glass-formers include pure oxides (SiO 2 , B 2 O 3 , GeO 2 ) [30,151], borates [18,64,67,76,78,151,152,153], silicates [18,89,152,154], aluminoborates [18], aluminoborosilicates [18,101], borosilicates [18,101], and tellurites [114,121,155]. For these systems, we highlight two observations.…”

Section: Resultsmentioning

confidence: 99%

Revisiting the Dependence of Poisson’s Ratio on Liquid Fragility and Atomic Packing Density in Oxide Glasses

et al. 2019

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Poisson’s ratio (ν) defines a material’s propensity to laterally expand upon compression, or laterally shrink upon tension for non-auxetic materials. This fundamental metric has traditionally, in some fields, been assumed to be a material-independent constant, but it is clear that it varies with composition across glasses, ceramics, metals, and polymers. The intrinsically elastic metric has also been suggested to control a range of properties, even beyond the linear-elastic regime. Notably, metallic glasses show a striking brittle-to-ductile (BTD) transition for ν-values above ~0.32. The BTD transition has also been suggested to be valid for oxide glasses, but, unfortunately, direct prediction of Poisson’s ratio from chemical composition remains challenging. With the long-term goal to discover such high-ν oxide glasses, we here revisit whether previously proposed relationships between Poisson’s ratio and liquid fragility (m) and atomic packing density (Cg) hold for oxide glasses, since this would enable m and Cg to be used as surrogates for ν. To do so, we have performed an extensive literature review and synthesized new oxide glasses within the zinc borate and aluminoborate families that are found to exhibit high Poisson’s ratio values up to ~0.34. We are not able to unequivocally confirm the universality of the Novikov-Sokolov correlation between ν and m and that between ν and Cg for oxide glass-formers, nor for the organic, ionic, chalcogenide, halogenide, or metallic glasses. Despite significant scatter, we do, however, observe an overall increase in ν with increasing m and Cg, but it is clear that additional structural details besides m or Cg are needed to predict and understand the composition dependence of Poisson’s ratio. Finally, we also infer from literature data that, in addition to high ν, high Young’s modulus is also needed to obtain glasses with high fracture toughness.

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Section: Resultsmentioning

confidence: 99%

Revisiting the Dependence of Poisson’s Ratio on Liquid Fragility and Atomic Packing Density in Oxide Glasses

et al. 2019

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“…Considering first the overall trend in Figure 5, a negative correlation between Poisson's ratio and nBO is seen as expected [7], but the range of Poisson's ratios at each nBO value is larger than that previously reported. To further investigate the role of network connectivity on Poisson's ratio, we revisit the ν-n BO correlation by replotting Figure 4 with literature values for a variety of alkali and alkaline earth silicate [45,49,[51][52][53], borosilicate [50,54,55], aluminosilicate [30,50,56,57], alkali borate [42,[58][59][60], and phosphate glasses [61][62][63][64] (Figure 5). Here, the boron and phosphorus containing glasses are new compared to the original study [7].…”

Section: Discussionmentioning

confidence: 99%

“…silicate [45,49,[51][52][53], borosilicate [50,54,55], aluminosilicate [30,50,56,57], alkali borate [42,[58][59][60], and phosphate glasses [61][62][63][64] (Figure 5). Here, the boron and phosphorus containing glasses are new compared to the original study [7].…”

Section: Discussionmentioning

confidence: 99%

“…Each atom in the glass has a number of constraints that can be divided into bond-bending and bond-stretching, which in turn can be calculated from the atomic coordination numbers [74]. We test the correlation for the glasses in this study as well as glasses from literature, namely alkali silicates [17,45,49], alkali borates [42,[58][59][60], alkaline earth silicates [51], and borosilicates, aluminosilicates, aluminoborates, and aluminoborosilicates [50]. The number of constraints are calculated differently.…”

Section: Discussionmentioning

confidence: 99%

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Structure Dependence of Poisson’s Ratio in Cesium Silicate and Borate Glasses

2020

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In glass materials, Poisson’s ratio (ν) has been proposed to be correlated with a variety of features, including atomic packing density (Cg), liquid fragility (m), and network connectivity. To further investigate these correlations in oxide glasses, here, we study cesium borate and cesium silicate glasses with varying modifier/former ratio given the difference in network former coordination and because cesium results in relatively high ν compared to the smaller alkali modifiers. Within the binary glass series, we find positive correlations between ν on one hand and m and Cg on the other hand. The network former is found to greatly influence the correlation between ν and the number of bridging oxygens (nBO), with a negative correlation for silicate glasses and positive correlation for borate glasses. An analysis based on topological constraint theory shows that this difference cannot be explained by the effect of superstructural units on the network connectivity in lithium borate glasses. Considering a wider range of oxide glasses from the literature, we find that ν generally decreases with increasing network connectivity, but with notable exceptions for heavy alkali borate glasses and calcium alumino tectosilicate glasses.

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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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Fragility and anharmonicity of lattice vibrations of glass-forming systems

Cited by 11 publications

References 10 publications

Revisiting the Dependence of Poisson’s Ratio on Liquid Fragility and Atomic Packing Density in Oxide Glasses

Revisiting the Dependence of Poisson’s Ratio on Liquid Fragility and Atomic Packing Density in Oxide Glasses

Structure Dependence of Poisson’s Ratio in Cesium Silicate and Borate Glasses

On relaxation nature of glass transition in amorphous materials

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