A molecular dynamics study of barium meta-fluorozirconate glass

Abstract

Molecular dynamics simulation was performed on barium meta-fluorozirconate, BaZrF6, glass by using the Born–Mayer–Huggins pair potential. The cumulative F coordination numbers and the F correlation functions of Zr and Ba ions revealed that, in the simulated BaZrF6 glass, the number and the mean distance of the nearest neighboring F were about eight at 2.12 Å for Zr ions and about ten at 2.75 Å for Ba ions. This is consistent with the previous x-ray diffraction result of the glass. A little uncertainty of the cumulative coordination number, however, may admit the presence of small amounts of seven F-coordinated Zr, as deduced in the previous studies. On the other hand, the Zr–Zr pair correlation function disclosed that the F polyhedra of Zr are linked by sharing the edges and/or the corners, the edge-sharing/corner-sharing ratio in number being approximately 3:2. The glass transition temperature and the Zr–F symmetric stretching vibration spectrum generated for the simulated glass were favorably compared with the observed ones. The mean square displacements and the trajectories of F, Zr, and Ba ions clearly showed that fluorozirconate glasses might exhibit fluoride-ion conduction. The present successful simulation indicates the validity of the calculation procedure, especially of the evaluation of the repulsive parameters of Zr and Ba ions. Based on the previous Raman spectroscopy, differential thermal analysis, and x-ray diffraction studies and the present study, the overall structure of BaZrF6 may be described as follows: In BaZrF6 glass, most of Zr ions are dodecahedrally coordinated by eight F and a small amount of them, monocapped-trigonal prismatically by seven F. These polyhedra connect with each other by sharing the edges and/or corners to build up three-dimensional fluorozirconate network. Ba ions are present as the modifier ions in the interstices of the fluorozirconate network, being surrounded on the average by ten F.