Short-Range Structure of Vitreous P₂O₅ by MD Simulation

Abstract

We have performed molecular dynamics (MD) simulations for vitreous P₂O₅ using isotropic pair potentials composed only of coulombic and repulsive interactions. The P–O pair distribution function obtained had the two distinguishable peaks expected from the results of neutron diffraction experiments, in the nearest-neighbor P–O correlation. The neutron-weighted real-space correlation function was also in semi-quantitative agreement with that obtained from the experimental results. The distribution of the coordination number for O around P and P around O showed that most P atoms form tetrahedral PO₄ units in the glass, and that three-fifths of O atoms are bridging oxygen atoms, O_B, and the remaining are terminal oxygen atoms, O_T. The pair distribution functions for P–O_B and P–O_T show that the PO₄ units have three long P–O_B bonds and one short P–O_T bond. We have concluded that the short-range structure obtained for vitreous P₂O₅ agrees well with the picture derived from many experiments. This fact indicates that the short-range structure of vitreous P₂O₅ can be described mainly by both charge ordering and packing based on the differences in ionic charge and size between cation and anion.