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- Structure and vibrational properties of sodium silicate glass surfaces doi link

Auteur(s): Zhang Z., Ispas S., Kob W.(Corresp.)

(Article) Publié: The Journal Of Chemical Physics, vol. 153 p.124503 (2020)
Texte intégral en Openaccess : arxiv


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.