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(11) Production(s) de ZHANG Z.
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Intermediate-range order governs dynamics in dense colloidal liquids
Auteur(s): Singh Navneet, Zhang Z., Sood A.k., Kob W., Ganapathy Rajesh
(Article) Publié:
Proceedings Of The National Academy Of Sciences Of The United States Of America, vol. 120 p.e2300923120 (2023)
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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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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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Structure and vibrational properties of sodium silicate glass surfaces
Auteur(s): Zhang Z., Ispas S., Kob W.
(Article) Publié:
The Journal Of Chemical Physics, vol. 153 p.124503 (2020)
Texte intégral en Openaccess :
Ref HAL: hal-02986296_v1
DOI: 10.1063/5.0019514
Exporter : BibTex | endNote
Résumé: Using molecular dynamics simulations we investigate the dependence of the structuraland vibrational properties of the surfaces of sodo-silicate glasses on the sodium content as well as the nature of the surface. Two types of glass surfaces are considered:A melt-formed surface (MS) in which a liquid with a free surface has been cooleddown into the glass phase and a fracture surface (FS) obtained by tensile loadingof a glass sample. We find that the MS is more abundant in Na and non-bridgingoxygen atoms than the FS and the bulk glass, whereas the FS has higher concentration of structural defects such as two-membered rings and under-coordinated Si thanthe MS. We associate these structural differences to the production histories of theglasses and the mobility of the Na ions. It is also found that for Na-poor systems thefluctuations in composition and local atomic charge density decay with a power-lawas a function of distance from the surface while Na-rich systems show an exponentialdecay with a typical decay length of ≈ 2.3 Å. The vibrational density of states showsthat the presence of the surfaces leads to a decrease of the characteristic frequenciesin the system. The two-membered rings give rise to a pronounce band at ≈ 880 cm−1which is in good agreement experimental observations.
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