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Structure and diffusion in amorphous aluminium silicate: A molecular dynamics computer simulation | | Anke Winkler
; Jurgen Horbach
; Walter Kob
; Kurt Binder
; | | Date: |
10 May 2003 | | Subject: | Statistical Mechanics; Disordered Systems and Neural Networks | cond-mat.stat-mech cond-mat.dis-nn | | Affiliation: | Institute of Physics Mainz), Jurgen Horbach (Institute of Physics Mainz), Walter Kob (Laboratoire des Verres Montpellier), and Kurt Binder (Institute of Physics Mainz | | Abstract: | The amorphous aluminium silicate (Al2O3)2(SiO2) [AS2] is investigated by means of large scale molecular dynamics computer simulations. We consider fully equilibrated melts in the temperature range 6100K >= T >= 2300K as well as glass configurations that were obtained from cooling runs from T=2300K to 300K with a cooling rate of about 10^12K/s. Already at temperatures as high as 4000K, most of the Al and Si atoms are four-fold coordinated by oxygen atoms. Thus, the structure of AS2 is that of a disordered tetrahedral network. The packing of AlO4 tetrahedra is very different from that of SiO4 tetrahedra in that Al is involved with a relatively high probability in small-membered rings and in triclusters in which an O atom is surrounded by four cations. We find as typical configurations two-membered rings with two Al atoms in which the shared O atoms form a tricluster. On larger length scales, the system shows a microphase separation in which the Al-rich network structure percolates through the SiO2 network. The latter structure gives rise to a prepeak in the static structure factor at a wavenumber q=0.5AA^{-1}. The comparison of experimental X-ray data with the results from the simulation shows a good agreement for the structure function. The diffusion dynamics in AS2 is found to be much faster than in SiO2. We show that the self-diffusion constants for O and Al are very similar and that they are by a factor of 2-3 larger than the one for Si. | | Source: | arXiv, cond-mat/0305227 | | Services: | Forum | Review | PDF | Favorites | |
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