%0 Journal Article
%T Structure and diffusion in amorphous aluminium silicate: A molecular dynamics computer simulation
%+ Laboratoire des colloïdes, verres et nanomatériaux (LCVN)
%A Winkler, Anke
%A Horbach, Jurgen
%A Kob, Walter
%A Binder, Kurt
%Z 30 pages of Latex, 13 figures
%< avec comité de lecture
%@ 0021-9606
%J Journal of Chemical Physics
%I American Institute of Physics
%V 120
%P 394-393
%8 2004
%D 2004
%Z cond-mat/0305227
%Z Physics [physics]/Condensed Matter [cond-mat]/Statistical Mechanics [cond-mat.stat-mech]Journal articles
%X 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=0.5\Å^{-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.
%G English
%L hal-00012958
%U https://hal.science/hal-00012958
%~ CNRS
%~ UNIV-MONTP2
%~ LCVN
%~ UNIV-MONTPELLIER
%~ UM1-UM2