Cambridge 7th to 9th September
article posted 10 Mar 2015
Edwin Flikkema is a lecturer at the Department of Physics at Aberystwyth University in
Wales (United Kingdom). He works in the general field of computational materials science.
He is fairly new to the field of glass science. His other interests include the modelling of
polymers, nano-particles, zeolites and foams
Ion dynamics in alkali-silicates: a Molecular Dynamics study
Edwin Flikkema*, Wenlin Chen, Zhongfu Zhou, Neville Greaves
Department of Physics, Aberystwyth University, Penglais Campus,
Aberystwyth SY23 3BZ, United Kingdom
Silicates form an important class of glass-forming materials. Their structure can be
described as a network of silicon and oxygen atoms. This presentation focuses on
sodium-potassium-disilicates (i.e mixtures of
The introduction of alkali ions together with oxygen in the form of Na2
O or K2
leads to the formation of non-bridging oxygens, partially breaking the silicon-oxygen
network. Often, a static network is formed with pores in it, through which the alkali
ions are relatively free to move.
The Mixed Alkali Effect (MAE) is an experimentally found phenomenon where the
electrical conductivity as a function of alkali composition (Na to K ratio) is non-linear
and exhibits a minimum. One of the goals of this computational study is to replicate
the MAE in simulations and to be able to investigate it in atomic detail.
Sodium-potassium-disilicates with various Na to K ratios have been studied
computationally using Molecular Dynamics. Initial atomic configurations are
based on annealing from a high temperature molten phase. Simulations were
performed at a wide range of temperatures.
Static properties such as the radial distribution function and Q species distribution
were calculated from the simulations and compared to experiment.
The focus of this study is on dynamic properties, mainly on the dynamics of the
alkali ions. The mean square displacement of the ions as a function of time has
been studied and diffusion constants have been obtained. The intermediate structure
factor has been calculated and this has been analysed by modelling it as a stretched
Dynamic heterogeneity of the alkali ions is analysed. Advanced visualisation is used
to map out the free volume that is accessible by the alkali ions and to track the motion
of the ions in order to gain a deeper understanding of the MAE.