Atomic diffusion in covalent liquids under pressure fromab initiomolecular dynamics

S Ohmura,F Shimojo,R Yoshimura

doi:10.1051/epjconf/20111502003

S Ohmura, F Shimojo + Show 1 more

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https://doi.org/10.1051/epjconf/20111502003

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Abstract

2 Research Fellow of the Japan Society for the Promotion of Science Abstract. The microscopic mechanisms of atomic diffusion in liquid GeO2 and SrGeO3 are investigated by ab initio molecular-dynamics simulations. We clarify the differences of diffusion mechanism between liquid GeO2 and SrGeO3. In both liquids, non-bridging oxygen double bonded to only one germanate plays a key role in the atomic diffusion mechanism. It is found that, in liquid SrGeO3 which has non-bridging oxygen in the equilibrium state at ambient pressure, atomic diffusion is possible without generating overcoordinated atoms at ambient pressure, while the over coordinated atoms are always needed for the formation of non-bridging oxygens in liquid GeO2. When the pressure increases, only liquid GeO2 has a diffusion maximum, which is given by, the atomic diffusion with concerted reaction gives the diffusion maximum.

Highlights

Transport properties of covalent liquids under pressure are very interesting in the sense that they show unexpected pressure dependence
In liquid GeO2, Ge atoms are mainly coordinated to four O atoms and O atoms bridge two adjacent Ge atoms as in the crystalline phase, even though atoms diffuse in the liquid state
The microscopic mechanism of atomic diffusion in liquid GeO2 and SrGeO3 has been investigated by ab initio molecular-dynamics simulations

Summary

Introduction

Transport properties of covalent liquids under pressure are very interesting in the sense that they show unexpected pressure dependence. For a number of covalent liquids, such as SiO2, GeO2, silicates and germanates, abnormal behaviour of the viscosity has been observed, i.e. the viscosity significantly drops with pressure [1,2]. This anomalous behaviour of the viscosity is considered to be related to the atomic diffusion in the liquids under pressure. It is, of particular interest to explore the pressure dependence of the microscopic diffusion mechanism in covalent liquids. Becuse the calculated results obtained by emprical potentials depend on the choice of the potential form, theoretical investigations based on first-principles theory would be needed to clarify the microscopic mechanism of atomic diffusion in liquid state

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