Ion Dynamics in Pure and Mixed Alkali Glasses -Separation of the Spatial and Temporal Aspects-

Long time (∼1 ns region) molecular dynamics (MD) simulations of lithium metasilicate (Li 2 SiO 3 ) and a mixed alkali silicate (LiKSiO 3 ) glass have been performed to confirm the mechanism of the “mixed alkali effect,” which has been previously deduced from the shorter time behavior. In the Li 2 SiO 3 system, long time behavior of lithium ion has been characterized by a component showing the enhanced diffusion (Lévy flight) due to cooperative jumps. The main diffusion and conduction processes of silicate glasses are not the single jumps but the cooperative jumps. The component taking the accelerated dynamics is found to be nearly absent in the mixed alkali system. Contributions of both temporal and spatial aspects for the particle dynamics are separated. The large change in the spatial parameters has been observed on mixing. Interception of the jump path due to other kinds of ion path suppresses the cooperative jump process.