Defects and oxygen diffusion in metasilicate melts: Molecular dynamics simulation

Abstract

The specific features of the dynamics of oxygen ions in Me 2O ⋅ SiO2 (Me = Li, Na, K, Cs) melts at a temperature of 2000 K are investigated by the molecular dynamics method in the partially ionic potential approximation. It is demonstrated that, as in the systems studied earlier, the formation of defect complexes is a necessary condition for an oxygen diffusion event to be successful. The methods for generating defect complexes are described, and the lifetimes of these complexes are calculated. The structure of the defect complexes is determined. It is found that, in the Li2O ⋅ SiO2 melt, successful oxygen diffusion events occur predominantly with the participation of fivefold-coordinated silicon ions. The threefold-coordinated defects begin to predominate in the Na2O ⋅ SiO2 melt, and their role becomes crucial in the diffusion in the potassium and cesium metasilicate melts. It is shown for the first time that free and threefold-coordinated oxygen ions can also be involved in the formation of defect complexes.