From pockets to channels: Density-controlled diffusion in sodium silicates

Classical molecular dynamics is used to study the dynamics of sodium atoms in liquid Na2O-3SiO(2) (NS3) as a function of system density. It is found that diffusion displays different regimes with increasing density at fixed temperature: a channel- connected network at ambient pressures which reduces to small pockets once the density is increased. The obtained features can be further characterized by the probability of Na hopping that shows a percolative behavior at around 2.25 g/cm(3) at the lowest temperature of 1500 K, which correlates with a threshold in the coordination number of the silicon and oxygen atoms. These results highlight the fact that transport properties in simple silicates can be substantially modified under a limited density change.