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DF: Dielektrische Festkörper

DF 4: Gl
äser Ib (gemeinsam FV DF/DY)

DF 4.7: Vortrag

Dienstag, 25. März 2003, 11:45–12:00, HSZ/403

The structure and dynamics of binary silicate glasses and melts — Molecular dynamics simulations — •Anke Winkler¹, Jürgen Horbach¹, Walter Kob², and Kurt Binder¹ — ¹Institut für Physik, Staudinger Weg 7, Johannes Gutenberg–Universität, D–55099 Mainz, Germany — ²Laboratoire des Verres, Université Montpellier II, F–34095 Montpellier Cedex 05, France

We use large scale molecular dynamics computer simulations to investigate the structural and dynamical behaviour of silicate melts and glasses of the systems ’NSx’= (Na₂O)x(SiO₂), x=1.5,2,3,5,20,40, and ’AS2’=(Al₂O₃)2(SiO₂).
Na₂O acts as a network modifier, that partially breaks up the tetrahedral SiO₄ network formed in pure silica. As a consequence, an additional structure on an intermediate length scale is created, reflecting the formation of Na₂O rich regions. The well-known fact from experiments that the systems NSx are prototypes of ion conducting glasses is reproduced already in the melt in that the Na ions diffuse much faster than the Si and O atoms. We show that the Na ions move through channels in the Si–O network which are related to the aforementioned Na₂O rich regions.
In contrast to Na₂O, Al₂O₃ can be built into the Si–O network structure. AS2 reveals a linked polyhedral structure, which mainly consists of AlO₄ and SiO₄ units. The ordering of AlO₄ tetrahedra differs from that of the SiO₂ tetrahedra. The system shows a high content of typical 3(Si,Al)O₄ ’tri-cluster’ units. An Al-rich network structure percolates through the Si–O structure. AS2 can be characterized by very interesting dynamical features, which we will also discuss in detail.