Melts of many silicates are known to have an anomalous transport property in that the diffusivity of oxygen atoms drastically increases with pressure. Here we propose a mechanism for the anomalous diffusion process in liquid silica and silicates on the basis of molecular dynamics (MD) results for pressure-induced structural transformations in crystalline silica. The model is successfully tested with a MD simulation for liquid silica with an interatomic potential based on a first-principles calculation. A close relation between the diffusivity of oxygen atoms in molten state and the relative stability of polymorphs of silica is clarified.

• Received 27 October 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.3197