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(91) Production(s) de ISPAS S.
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Elaboration of a neural-network interatomic potential for silica glass and melt
Auteur(s): Trillot Salomé, Lam Julien, Ispas S., Kandy Akshay Krishna Ammothum, Tuckerman Mark, Tarrat Nathalie, Benoit Magali
(Article) Publié:
Computational Materials Science, vol. 236 p.112848 (2024)
Texte intégral en Openaccess :
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Surface properties of alkali silicate glasses: Influence of the modifiers
Auteur(s): Zhang Z., Ispas S., Kob W.
(Article) Publié:
The Journal Of Chemical Physics, vol. 158 p.244504 (2023)
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Fracture of silicate glasses: Micro-cavities and correlations between atomic-level properties
Auteur(s): Zhang Z., Ispas S., Kob W.
(Article) Publié:
Physical Review Materials, vol. 6 p.085601 (2022)
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Origin of the non-linear elastic behavior of silicate glasses
Auteur(s): Zhang Z., Ispas S., Kob W.
(Article) Publié:
Acta Materialia, vol. 231 p.117855 (2022)
Texte intégral en Openaccess :
Ref HAL: hal-03690843_v1
Ref Arxiv: 2111.09549
DOI: 10.1016/j.actamat.2022.117855
WoS: WOS:000793420000002
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: For small tension the response of a solid to an applied stress is given by Hooke’s law. Outside this linear regime the relation between stress and strain is no longer universal and at present there is no satisfactory insight on how to connect for disordered materials the stress-strain relation to the microscopic properties of the system. Here we use atomistic computer simulations to establish this connection for the case of silicate glasses containing alkali modifiers. By probing how in the highly non-linear regime the stress-strain curve depends on composition, we are able to identify the microscopic mechanisms that are responsible for the complex dependence of stress on strain in these systems, notably the presence of an unexpected quasi-plateau in the tangent modulus. We trace back this dependence to the mobility of the modifiers which, without leaving their cage or modifying the topology of the network, are able to relieve the local stresses. Since the identified mechanism is general, the results obtained in this study will also be helpful for understanding the mechanical response of other disordered materials.
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Percolation transitions in compressed SiO2 glasses
Auteur(s): Hasmy A., Ispas S., Hehlen B.
(Article) Publié:
Nature, vol. 599 p.62 (2021)
DOI: 10.1038/s41586-021-03918-0
Résumé: Amorphous–amorphous transformations under pressure are generally explained by
changes in the local structure from low- to higher-fold coordinated polyhedra1–4.
However, as the notion of scale invariance at the critical thresholds has not been
addressed, it is still unclear whether these transformations behave similarly to true
phase transitions in related crystals and liquids. Here we report ab initio-based
calculations of compressed silica (SiO2) glasses, showing that the structural changes
from low- to high-density amorphous structures occur through a sequence of
percolation transitions. When the pressure is increased to 82 GPa, a series of
long-range (‘infinite’) percolating clusters composed of corner- or edge-shared
tetrahedra, pentahedra and eventually octahedra emerge at critical pressures and
replace the previous ‘phase’ of lower-fold coordinated polyhedra and lower
connectivity. This mechanism provides a natural explanation for the well-known
mechanical anomaly around 3 GPa, as well as the structural irreversibility beyond
10 GPa, among other features. Some of the amorphous structures that have been
discovered mimic those of coesite IV and V crystals reported recently5,6, highlighting
the major role of SiO5 pentahedron-based polyamorphs in the densification process of
vitreous silica. Our results demonstrate that percolation theory provides a robust
framework to understand the nature and pathway of amorphous–amorphous
transformations and open a new avenue to predict unravelled amorphous solid states
and related liquid phases7,8.
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New interaction potentials for alkaline earth silicate and borate glasses
Auteur(s): Shih Yueh-Ting, Sundararaman Siddharth, Ispas S., Huang Liping
(Article) Publié:
Journal Of Non-Crystalline Solids, vol. 565 p.120853 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03323812_v1
DOI: 10.1016/j.jnoncrysol.2021.120853
WoS: WOS:000663076400005
Exporter : BibTex | endNote
Résumé: New interaction potentials were developed for molecular dynamics simulations to study the role of Mg and Ca in modifying the structure and properties of alkaline earth silicates and borates. Competition between the depolymerization of the silica network and the formation of new bonds between oxygen atoms and modifiers leads to the enhancement of the elastic moduli with increasing modifier content in alkaline earth silicate glasses. Compared with calcium silicate, the higher elastic moduli of magnesium silicate result from a higher connectivity of the overall glass network due to the incorporation of fourfold coordinated magnesium and a more rigid connection between oxygen atoms and modifiers. In contrast to the silicates, the effect of modifier on the elastic moduli of alkaline earth borates is dominated by the formation of fourfold coordinated boron (N4). Calcium borate with higher N4 shows a more rigid network structure and higher elastic moduli.
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First-principles study of the surface of silica and sodium silicate glasses
Auteur(s): Zhang Z., Kob W., Ispas S.
(Article) Publié:
Physical Review B, vol. 103 p.184201 (2021)
Texte intégral en Openaccess :
Ref HAL: hal-03223925_v1
DOI: 10.1103/PhysRevB.103.184201
Exporter : BibTex | endNote
Résumé: We use ab initio molecular dynamics simulations to investigate the properties of the dry surface of pure silicaand sodium silicate glasses. The surface layers are defined based on the atomic distributions along the direction(z direction) perpendicular to the surfaces. We show that these surfaces have a higher concentration of danglingbonds as well as two-membered (2M) rings than the bulk samples. Increasing the concentration of Na 2 O reducesthe proportion of structural defects. From the vibrational density of states, one concludes that 2M rings have aunique vibrational signature at a frequency ≈850 cm −1 , compatible with experimental findings. We also findthat, due to the presence of surfaces, the atomic vibration in the z direction is softer than for the two otherdirections. The electronic density of states shows clearly the differences between the surface and interior and wecan attribute these to specific structural units. Finally, the analysis of the electron localization function allows toget insight on the influence of local structure and the presence of Na on the nature of chemical bonding in theglasses.
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