Anomalies of the first sharp diffraction peak in network glasses: Evidence for correlations with dynamic and rigidity properties

Micoulaut, Matthieu; Bauchy, Mathieu

doi:10.1002/pssb.201248512

Cited by 64 publications

(65 citation statements)

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“…The corresponding activation energies E A display a similar minimum with pressure 9 , and when represented as a function of the calculated number of constraints, it is found that the minimum in E A coincides with n c ¼ 3 (top inset of Fig. 5a).…”

Section: Glass Transition Cyclementioning

confidence: 63%

“…The system under investigation is composed of 3,000 atoms that interact via a Born-Mayer pair-wise potential (J. Teter, unpublished results), which has been found to accurately reproduce experimental data on structure and dynamics [7][8][9] . Simulations have been performed both in (N, V, T) with 1.6 g cm À 3 oro4.2 g cm À 3 (for example, Fig.…”

Section: Methodsmentioning

confidence: 99%

“…To establish our conclusions, we use as a target system a densified sodium silicate liquid (2SiO 2 -Na 2 O or NS2) that is investigated by MD in (N, V, T) and (N, P, T) ensembles (see Methods Summary in refs [7][8][9]. These materials are made of SiO 4/2 tetrahedra that are connected by bridging oxygens (BOs) whereas sodium cations create in their immediate vicinity so-called non-BOs (NBO), which contribute to the depolymerization of the network structure (Fig.…”

Section: Glass Transition Cyclementioning

confidence: 99%

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Densified network glasses and liquids with thermodynamically reversible and structurally adaptive behaviour

2015

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If crystallization can be avoided during cooling, a liquid will display a substantial increase of its viscosity, and will form a glass that behaves as a solid with a relaxation time that grows exponentially with decreasing temperature. Given this 'off-equilibrium' nature, a hysteresis loop appears when a cooling/heating cycle is performed across the glass transition. Here we report on molecular dynamics simulations of densified glass-forming liquids that follow this kind of cycle. Over a finite pressure interval, minuscule thermal changes are found, revealing glasses of 'thermally reversible' character with optimal volumetric or enthalpic recovery. By analysing the topology of the atomic network structure, we find that corresponding liquids adapt under the pressure-induced increasing stress by experiencing larger bond-angle excursions. The analysis of the dynamic behaviour reveals that the structural relaxation time is substantially reduced in these adaptive liquids, and also drives the reversible character of the glass transition. Ultimately, the results substantiate the notion of stress-free (Maxwell isostatic) rigidity in disordered molecular systems, while also revealing new implications for the topological engineering of complex materials.

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Section: Glass Transition Cyclementioning

confidence: 63%

Section: Methodsmentioning

confidence: 99%

Section: Glass Transition Cyclementioning

confidence: 99%

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Densified network glasses and liquids with thermodynamically reversible and structurally adaptive behaviour

2015

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“…The correlation with chemical order is also debated by Boolchand and others who have emphasized the link between fragility minima and Figure 6. Correlation between relaxation properties, calculated diffusivity D (blue) and activation energy E A for diffusivity (red axis of the upper panels), and structural properties in the glassy state (black curve, width ∆k F SDP of the FSDP) in systems with changing pressure (2SiO 2 -Na 2 O, [69,70], left panels) or changing composition (As-Se, [71], right panels). Note that for As-Se, an opposite behavior for ∆k F SDP with composition is found from Reverse Monte Carlo [72].…”

Section: Qualitative Fragility Relationshipsmentioning

confidence: 99%

Relaxation and physical aging in network glasses: a review

Micoulaut

2016

Rep. Prog. Phys.

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Abstract. Recent progresses in the description of glassy relaxation and ageing are reviewed for the wide class of network-forming materials such as GeO 2 , Ge x Se 1−x , silicates (SiO 2 -Na 2 O) or borates (B 2 O 3 -Li 2 O), all of them having an important usefulness in domestic, geological or optoelectronic applications. A brief introduction of the glass transition phenomenology is given, together with the salient features that are revealed both from theory and experiments. Standard experimental methods used for the characterization of the slowing down of the dynamics are reviewed. We then discuss the important role played by aspect of network topology and rigidity for the understanding of the relaxation of the glass transition, while also permitting analytical predictions of glass properties from simple and insightful models based on the network structure. We also emphasize the great utility of computer simulations which probe the dynamics at the molecular level, and permit to calculate various structure-related functions in connection with glassy relaxation and the physics of ageing which reveals the off-equilibrium nature of glasses. We discuss the notion of spatial variations of structure which leads to the picture of "dynamic heterogeneities", and recent results of this important topic for network glasses are also reviewed.PACS numbers: 61.43. Fs, 64.70.kj Relaxation and physical ageing in network glasses 2 Figure 1. Typical network-forming glasses: a) A stoichiometric glass former (SiO 2 , B 2 S 3 ) whose structure and network connectivity can be altered by the addition (b) of 2-fold coordinated atoms (usually chalcogens, S, Se) that lead to cross-linked chains. The structure can also be depolymerized (c) by the addition of a network modifier (alkali oxides or chalcogenides, Na 2 O, Li 2 S, etc.). Glassy dynamics depends strongly on the network topology, i.e. the way bonds and angles arrange to lead to a connected atomic network. Note that only chalcogenides can produce a mixture of these three kinds of basic networks, e.g. (1-x)Ge y Se 1−y -xAg 2 Se [2], and for the latter system x=0 corresponds to case (b), y=33% corresponds to case (c), and both conditions together (x=0,y=33 %) to case (a).

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“…Neutron structure factor Figure 7 shows the total neutron structure factor for C-S-H as well as for the corresponding crystal and glass. Once again, the three structure factors do not show significant differences and are typical of those observed in silicate 36 and chalcogenide 37 glasses. It should be mentioned that the limited sizes of the simulated systems do not allow us to study large-scale correlations (large r, low Q).…”

Section: Medium-range Ordermentioning

confidence: 52%

Order and disorder in calcium–silicate–hydrate

Bauchy

Qomi

Ulm

et al. 2014

The Journal of Chemical Physics

108

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Quasielastic and inelastic neutron scattering on hydrated calcium silicate pastes J. Chem. Phys. 121, 3212 (2004) Despite advances in the characterization and modeling of cement hydrates, the atomic order in Calcium-Silicate-Hydrate (C-S-H), the binding phase of cement, remains an open question. Indeed, in contrast to the former crystalline model, recent molecular models suggest that the nanoscale structure of C-S-H is amorphous. To elucidate this issue, we analyzed the structure of a realistic simulated model of C-S-H, and compared the latter to crystalline tobermorite, a natural analogue of C-S-H, and to an artificial ideal glass. The results clearly indicate that C-S-H appears as amorphous, when averaged on all atoms. However, an analysis of the order around each atomic species reveals that its structure shows an intermediate degree of order, retaining some characteristics of the crystal while acquiring an overall glass-like disorder. Thanks to a detailed quantification of order and disorder, we show that, while C-S-H retains some signatures of a tobermoritelike layered structure, hydrated species are completely amorphous. © 2014 AIP Publishing LLC.

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Anomalies of the first sharp diffraction peak in network glasses: Evidence for correlations with dynamic and rigidity properties

Cited by 64 publications

References 50 publications

Densified network glasses and liquids with thermodynamically reversible and structurally adaptive behaviour

Densified network glasses and liquids with thermodynamically reversible and structurally adaptive behaviour

Relaxation and physical aging in network glasses: a review

Order and disorder in calcium–silicate–hydrate

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