Investigation of the structure of lithium borate ionic glasses

Christoph Tietz

Alkali borate glasses are well known fast ion conductors with various applications. Lithium borate glasses show the highest mobility between alkali borates and are eligible candidate for studying fast ionic motion mechanisms in glasses. The preferred new experimental technique for such studies is called atomic scale X-ray photon correlation spectroscopy (aXPCS).
As outlined in the brief introduction into aXPCS given by Ross[9], knowledge of the ion-ion partial structure factor is essential for the data analysis of the aXPCS measurement. The investigation of the short-range order of lithium borate glasses is therefore seen in the prospect of future aXPCS measurements previously performed for rubidium[10], potassium and sodium borate glasses.
The goal of this Master’s thesis was to perform preliminary experimental studies and computer simulations of short-range order (SRO) of lithium borate glasses as an introductory stage for future synchrotron experiments. SRO of lithium borate glasses was investigated by X-ray scattering. Three lithium glass samples with different alkali content were prepared in our laboratory and investigated by small-angle X-ray scattering (SAXS) as well as wide-angle X-ray scattering (WAXS) techniques. Measuring with the WAXS set-up allowed the measurement of the first two diffraction peaks. Not too much quantitative results could be extracted from the SAXS measurement yet some qualitative information about large scale inhomogeneities have been gained.
The Monte Carlo simulations allow detailed investigation of structural properties like spatial correlations, angle distributions, coordination number, the abundance of tetrahedrally coordinated boron atoms, partial structure factors and the Faber-Ziman structure factor. A well established Born-Mayer-Huggins type pair potential in conjunction with a three-body potential was used to run Monte Carlo simulations in the canonical ensemble. Different quantities obtained from my simulations were compared with literature results, both experimental and simulated using Molecular Dynamics (MD) method. Similarities and discrepancies between these methods, i.e. between MC and MD technique, allowed to draw interesting conclusions about strengths and weaknesses of both types of computer simulations.

Dynamik Kondensierter Systeme
Anzahl der Seiten
ÖFOS 2012
103018 Materialphysik, 103009 Festkörperphysik, 103015 Kondensierte Materie
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