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22 pages, 2479 KB

Open AccessReview

Role of Structural Changes at Vitrification and Glass–Liquid Transition

by Michael I. Ojovan and Dmitri V. Louzguine-Luzgin

Materials 2025, 18(16), 3886; https://doi.org/10.3390/ma18163886 - 19 Aug 2025

Cited by 3 | Viewed by 1320

Structural rearrangements at calorimetric glass transition are behind drastic changes of material characteristics, causing differences between glasses and melts. Structural description of materials includes both species (atoms, molecules) and connecting bonds, which are directly affected by changing conditions such as the increase of [...] Read more.

Structural rearrangements at calorimetric glass transition are behind drastic changes of material characteristics, causing differences between glasses and melts. Structural description of materials includes both species (atoms, molecules) and connecting bonds, which are directly affected by changing conditions such as the increase of temperature. At and above the glass transition a macroscopic percolation cluster made up of configurons (broken bonds) is formed, an account of which enables unambiguous structural differentiation of glasses from melts. Connection of transition caused by configuron percolation is also discussed in relation to the Noether theorem, Anderson localisation, and melting criteria of condensed matter. Full article

(This article belongs to the Section Advanced and Functional Ceramics and Glasses)

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21 pages, 4916 KB

Open AccessArticle

NiTi₂, a New Liquid Glass

by Robert F. Tournier and Michael I. Ojovan

Materials 2023, 16(20), 6681; https://doi.org/10.3390/ma16206681 - 13 Oct 2023

Cited by 5 | Viewed by 1791

Abstract

Many endothermic liquid–liquid transitions, occurring at a temperature T_n+ above the melting temperature T_m, are related to previous exothermic transitions, occurring at a temperature T_x after glass formation below T_g, with or without attached crystallization and predicted [...] Read more.

Many endothermic liquid–liquid transitions, occurring at a temperature T_n+ above the melting temperature T_m, are related to previous exothermic transitions, occurring at a temperature T_x after glass formation below T_g, with or without attached crystallization and predicted by the nonclassical homogenous nucleation equation. A new thermodynamic phase composed of broken bonds (configurons), driven by percolation thresholds, varying from ~0.145 to Δε, is formed at T_x, with a constant enthalpy up to T_n+. The liquid fraction Δε is a liquid glass up to T_n+. The solid phase contains glass and crystals. Molecular dynamics simulations are used to induce, in NiTi₂, a reversible first-order transition by varying the temperature between 300 and 1000 K under a pressure of 1000 GPa. Cooling to 300 K, without applied pressure, shows the liquid glass presence with Δε = 0.22335 as memory effect and T_n+ = 2120 K for T_m = 1257 K. Full article

(This article belongs to the Special Issue Multiscale Simulation of Advanced Materials: Microstructure Evolution and Mechanical Analysis)

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15 pages, 2210 KB

Open AccessArticle

The Flow of Glasses and Glass–Liquid Transition under Electron Irradiation

by Michael I. Ojovan

Int. J. Mol. Sci. 2023, 24(15), 12120; https://doi.org/10.3390/ijms241512120 - 28 Jul 2023

Cited by 14 | Viewed by 2500

Abstract

Recent discovery and investigation of the flow of glasses under the electron beams of transmission electron microscopes raised the question of eventual occurrence of such type effects in the vitrified highly radioactive nuclear waste (HLW). In connection to this, we analyse here the [...] Read more.

Recent discovery and investigation of the flow of glasses under the electron beams of transmission electron microscopes raised the question of eventual occurrence of such type effects in the vitrified highly radioactive nuclear waste (HLW). In connection to this, we analyse here the flow of glasses and glass–liquid transition in conditions of continuous electron irradiation such as under the e-beam of transmission electron microscopes (TEM) utilising the configuron (broken chemical bond) concept and configuron percolation theory (CPT) methods. It is shown that in such conditions, the fluidity of glasses always increases with a substantial decrease in activation energy of flow at low temperatures and that the main parameter that controls this behaviour is the dose rate of absorbed radiation in the glass. It is revealed that at high dose rates, the temperature of glass–liquid transition sharply drops, and the glass is fully fluidised. Numerical estimations show that the dose rates of TEM e-beams where the silicate glasses were fluidised are many orders of magnitude higher compared to the dose rates characteristic for currently vitrified HLW. Full article

(This article belongs to the Special Issue Glass Transition and Related Phenomena 2.0)

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17 pages, 3652 KB

Open AccessArticle

Multiple Glass Transitions in Bismuth and Tin beyond Melting Temperatures

by Robert F. Tournier

Metals 2022, 12(12), 2085; https://doi.org/10.3390/met12122085 - 5 Dec 2022

Cited by 3 | Viewed by 2820

Abstract

Liquid-liquid transitions were discovered above the melting temperature (T_m) in Bi and Sn up to 2 T_m, viewed as glass transitions at T_g = T_n+ > T_m of composites nucleated at T_x < T_m [...] Read more.

Liquid-liquid transitions were discovered above the melting temperature (T_m) in Bi and Sn up to 2 T_m, viewed as glass transitions at T_g = T_n+ > T_m of composites nucleated at T_x < T_m and fully melted at T_n+. A glassy fraction (f) disappeared at 784 K in Sn. (T_n+) increases with singular values of (f) depending on T_x with (f) attaining 100% at T_g = T_n+ = 2 T_m. The nonclassical model of homogeneous nucleation is used to predict T_x, T_n+ and the specific heat. The singular values of (f) leading to (T_n+) correspond to percolation thresholds of configurons in glassy phases. A phase diagram of glassy fractions occurring in molten elements is proposed. The same value of (T_x) can lead to multiple (T_g). Values of (T_g = T_n₊) can be higher than (2 T_m) for T_x/T_m < 0.7069. A specific heat equal to zero is predicted after cooling from T ≤ 2 T_m and would correspond to a glassy phase. Weak glassy fractions are nucleated near (T_n+) after full melting at (T_m) without transition at (T_x). Resistivity decreases were observed after thermal cycling between solid and liquid states with weak and successive values of (f) due to T_x/T_m < 0.7069. Full article

(This article belongs to the Section Crystallography and Applications of Metallic Materials)

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18 pages, 16526 KB

Open AccessArticle

Multiple Melting Temperatures in Glass-Forming Melts

by Robert F. Tournier and Michael I. Ojovan

Sustainability 2022, 14(4), 2351; https://doi.org/10.3390/su14042351 - 18 Feb 2022

Cited by 8 | Viewed by 3392

Abstract

All materials are vitrified by fast quenching even monoatomic substances. Second melting temperatures accompanied by weak exothermic or endothermic heat are often observed at T_n+ after remelting them above the equilibrium thermodynamic melting transition at T_m. These temperatures, T_n+ [...] Read more.

All materials are vitrified by fast quenching even monoatomic substances. Second melting temperatures accompanied by weak exothermic or endothermic heat are often observed at T_n+ after remelting them above the equilibrium thermodynamic melting transition at T_m. These temperatures, T_n+, are due to the breaking of bonds (configurons formation) or antibonds depending on the thermal history, which is explained by using a nonclassical nucleation equation. Their multiple existence in monoatomic elements is now demonstrated by molecular dynamics simulations and still predicted. Proposed equations show that crystallization enthalpy is reduced at the temperature T_x due to new vitrification of noncrystallized parts and their melting at T_n+. These glassy parts, being equal above T_x to singular values or to their sum, are melted at various temperatures T_n+ and attain 100% in Cu₄₆Zr₄₆Al₈ and 86.7% in bismuth. These first order transitions at T_n+ are either reversible or irreversible, depending on the formation of super atoms, either solid or liquid. Full article

(This article belongs to the Section Sustainable Materials)

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10 pages, 2029 KB

Open AccessArticle

On Structural Rearrangements during the Vitrification of Molten Copper

by Michael I. Ojovan and Dmitri V. Louzguine-Luzgin

Materials 2022, 15(4), 1313; https://doi.org/10.3390/ma15041313 - 10 Feb 2022

Cited by 16 | Viewed by 2676

Abstract

We utilise displacement analysis of Cu-atoms between the chemical bond-centred Voronoi polyhedrons to reveal structural changes at the glass transition. We confirm that the disordered congruent bond lattice of Cu loses its rigidity above the glass transition temperature (T_g) in [...] Read more.

We utilise displacement analysis of Cu-atoms between the chemical bond-centred Voronoi polyhedrons to reveal structural changes at the glass transition. We confirm that the disordered congruent bond lattice of Cu loses its rigidity above the glass transition temperature (T_g) in line with Kantor–Webman theorem due to percolation via configurons (broken Cu-Cu chemical bonds). We reveal that the amorphous Cu has the T_g = 794 ± 10 K at the cooling rate q = 1 × 10¹³ K/s and that the determination of T_g based on analysis of first sharp diffraction minimum (FDSM) is sharper compared with classical Wendt–Abraham empirical criterion. Full article

(This article belongs to the Special Issue Feature Paper Collection of Topical Advisory Members)

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17 pages, 2139 KB

Open AccessEditor’s ChoiceArticle

On Structural Rearrangements Near the Glass Transition Temperature in Amorphous Silica

by Michael I. Ojovan and Robert F. Tournier

Materials 2021, 14(18), 5235; https://doi.org/10.3390/ma14185235 - 11 Sep 2021

Cited by 38 | Viewed by 4742

Abstract

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 [...] Read more.

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 T_g. 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 T_g 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 formation of ferromagnetic or superconducting phases when the more ordered phase is located below the transition threshold, the configuron phase was located above it. Full article

(This article belongs to the Section Materials Physics)

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14 pages, 1713 KB

Open AccessReview

The Modified Random Network (MRN) Model within the Configuron Percolation Theory (CPT) of Glass Transition

by Michael I. Ojovan

Ceramics 2021, 4(2), 121-134; https://doi.org/10.3390/ceramics4020011 - 29 Mar 2021

Cited by 27 | Viewed by 6302

Abstract

A brief overview is presented of the modified random network (MRN) model in glass science emphasizing the practical outcome of its use. Then, the configuron percolation theory (CPT) of glass–liquid transition is concisely outlined, emphasizing the role of the actual percolation thresholds observed [...] Read more.

A brief overview is presented of the modified random network (MRN) model in glass science emphasizing the practical outcome of its use. Then, the configuron percolation theory (CPT) of glass–liquid transition is concisely outlined, emphasizing the role of the actual percolation thresholds observed in a complex system. The MRN model is shown as an important tool enabling to understand within CPT the reduced percolation threshold in complex oxide systems. Full article

(This article belongs to the Special Issue What Do We Still Want to Know 90 Years After the Continuous Random Network (CRN) Theory?)

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31 pages, 1075 KB

Open AccessArticle

Configurons: Thermodynamic Parameters and Symmetry Changes at Glass Transition

by Michael I. Ojovan

Entropy 2008, 10(3), 334-364; https://doi.org/10.3390/e10030334 - 24 Sep 2008

Cited by 87 | Viewed by 16375

Abstract

Thermodynamic parameters of configurons – elementary excitations resulting from broken bonds in amorphous materials – are found from viscosity-temperature relationships. Glass-liquid transition phenomena and most popular models are described along with the configuron model of glass transition. The symmetry breaking, which occurs as [...] Read more.

Thermodynamic parameters of configurons – elementary excitations resulting from broken bonds in amorphous materials – are found from viscosity-temperature relationships. Glass-liquid transition phenomena and most popular models are described along with the configuron model of glass transition. The symmetry breaking, which occurs as a change of Hausdorff dimension of bonds, is examined at glass-liquid transition. Thermal history effects in the glass-liquid transition are interpreted in terms of configuron relaxation. Full article

(This article belongs to the Special Issue Configurational Entropy)

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