Regensburg 2007 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 30: Poster II

DY 30.42: Poster

Thursday, March 29, 2007, 16:00–18:00, Poster D

The description of ion dynamics in silicate glasses in terms of energy landscapes — •Heiko Lammert and Andreas Heuer — Westfälische Wilhelms-Universität, Institut für Physikalische Chemie, Corrensstr. 30, D-48149 Münster

A hopping picture is widely accepted for the description of ion dynamics in amorphous solids. The underlying energy landscape for ionic motion is highly complex due to the disordered structure of the materials, and also because of the changing Coulomb interactions between the mobile ions.

Computer simulations have shown that the Coulomb interaction is required for a completely correct reproduction of e. g. the Mixed Alkali Effect. Meanwhile many qualitative theories of the ion dynamics neglect the Coulomb interactions and work with independent particles and perfectly random distributions of energies and barriers.

We test these common assumptions using realistic molecular dynamics simulations of alkali silicates. Our method for the identification of individual ionic sites from the trajectories enables a treatment in terms of ion hopping. A new analysis of different contributions to the site energies allows a direct comparison to models using simplified energy landscapes.

The results demonstrate the important role of the Coulomb interaction for the fundamental behavior of the system. However the simple picture of independent particles on a random landscape can be recovered, when vacancies are treated instead of ions.