First principles study of a sodium borosilicate glass-former I: The liquid state

Abstract

We use ab initio simulations to study the static and dynamic properties of a sodium borosilicate liquid with composition 3Na_2O-B_2O_3-6SiO_2, i.e. a system that is the basis of many glass-forming materials. In particular we focus on the question how boron is embedded into the local structure of the silicate network liquid. From the partial structure factors we conclude that there is a weak nanoscale phase separation between silicon and boron and that the sodium atoms form channel-like structures as they have been found in previous studies of sodo-silicate glass-formers. Our results for the X-ray and neutron structure factor show that this feature is basically unnoticeable in the former but should be visible in the latter as a small peak at small wave-vectors. At high temperatures we find a high concentration of three-fold coordinated boron atoms which decreases rapidly with decreasing T, whereas the number of four-fold coordinated boron atoms increases. Therefore we conclude that at the experimental glass transition temperature most boron atoms will be four-fold coordinated. We show that the transformation of [3]B into [4]B with decreasing T is not just related to the diminution of non-bridging oxygen atoms as claimed in previous studies, but to a restructuration of the silicate matrix. The diffusion constants of the various elements show an Arrhenius behavior and we find that the one for boron has the same value as the one of oxygen and is significantly larger than the one of silicon. This shows that these two network formers have rather different dynamical properties, a result that is also confirmed from the time dependence of the van Hove functions. Finally we show that the coherent intermediate scattering function for the sodium atoms is very different from the incoherent one and that it tracks the one of the matrix atoms.

15 pages; 14 figures

References in corpus (6)

• Restoring the density-gradient expansion for exchange in solids and surfaces
• Generalized gradient approximation for solids and their surfaces
• Universal nature of particle displacements close to glass and jamming transitions
• First principles study of a sodium borosilicate glass-former II: The glass state
• Molecular dynamics computer simulation of amorphous silica under high pressure
• Comparative classical and ab initio Molecular Dynamics study of molten and glassy germanium dioxide

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• First principles study of a sodium borosilicate glass-former II: The glass state
• New interaction potentials for borate glasses with mixed network formers
• Vibrational properties of sodosilicate glasses from first-principles calculations
• New interaction potentials for alkaline earth silicate and borate glasses
• First principles study of the surface of silica and sodium silicate glasses
• Slowly Quenched, High Pressure Glassy B${}_2$O${}_3$ at DFT Accuracy
• On the Boroxol Ring Fraction in Melt-Quenched B${}_2$O${}_3$ Glass