• Tietz, Christoph

Abstract

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

Topics

• impedance spectroscopy
• mobility
• experiment
• simulation
• glass
• glass
• molecular dynamics
• strength
• Sodium
• Potassium
• Boron
• Lithium
• small angle x-ray scattering
• wide-angle X-ray scattering
• Rubidium