Glass - Back to the Future!

Presenting Author:
Edwin Flikkema

article posted 21 March

Edwin Flikkema is a lecturer at the Department of Physics at Aberystwyth University in Wales in the United Kingdom. Born in the Netherlands, he studied theoretical physics at the University of Groningen. He obtained a PhD (on the subject of Monte Carlo simulation in polymer physics) from the same university in 2002. He has worked as a postdoc at Delft University of Technology, the University of Barcelona and the University of Cambridge. Since 2008 he is working at Aberystwyth University, specialising in computational materials science: structure prediction of atomic clusters, simulation of glass-forming materials and foams.

Molecular Dynamics simulation of ion motion in alkali-silicates

Edwin Flikkema*, Wenlin Chen, Zhongfu Zhou, Neville Greaves
Department of Physics, IMPACS, Aberystwyth University, United Kingdom

This study is about ion mobility in alkali-silicates. An alkali-silicate is a glass-forming silicate material with network modifiers such as Sodium and Potassium added to it. The excess oxygen introduced by adding Na2O or K2O gives rise to non-bridging oxygens, leading to a partial break-up of the silica network. It is hypothesised that channels are formed where the alkali ions are relatively free to move. This Molecular Dynamics (MD) study focusses on the mobility of Sodium and Potassium ions in mixtures of Sodium-disilicate (Na2O-(SiO2)2) and Potassium-disilicate (K2O-(SiO2)2). It is found experimentally that ion-conductivity does not vary linearly with the Sodium/Potassium ratio. Rather, it exhibits a minimum, roughly at 50%/50%. This is known as the Mixed Alkali Effect (MAE). One of the aims of this study is to investigate whether this effect can be replicated in MD simulations. Our results show a MAE with respect to ion diffusion. The ion-dynamics is analysed in various ways, such as mean-square displacement and intermediate scattering functions. Dynamic heterogeneity is also considered. Advanced visualisation is used as a tool to help find the underlying mechanisms to ion motion.