Structural transformation and anomalous diffusion in network forming liquid GeO2

Abstract

In this study, we simulated the structural transformation and self-diffusion mechanism in liquid GeO₂ oxide system. Under compression, structure of liquid GeO₂ model tends to transform gradually from low-density phase to high-density phase. Concentration of basic structural units can be determined via density of material model. The average Ge-O bond distance in GeO₄ tetrahedra is smaller than the ones in GeO₅ pentahedra and GeO₆ octahedra. Each GeO_x polyhedron always exists a Ge-O bond with the longest length (the weakest bond). The diffusion mechanism in liquid GeO₂ Oxide system is via the breaking the weakest bonds that accompanying the change local coordination environment of Ge cations. The longest Ge-O bond in a GeO₅ pentahedron is very weak in comparison to the one in other polyhedra. The diffusivity is significantly dependent on the number of GeO₅ pentahedra. The increase of GeO₅ under compression is the origin of anomalous diffusion in liquid GeO₂ oxide. The increase of average Ge-O bond distance under compression is also clarified in this work.