Molecular dynamics study of glass formation in the system ZrF₄ - BaF₂ - BaCl₂ - MCl₂ (M = Mg, Ca, Sr)

Molecular dynamics calculations have been carried out on the system ZrF₄ - BaF₂ - BaCl₂ - MCl₂ (M = Mg, Ca, Sr). The emphasis has been laid on the investigation of the relation between the glass forming tendency and the distribution of Cl^- ions among the cation coordination spheres. In all the systems the average coordination numbers of F^- and Cl^- ions, N_F and N_Cl, around the cations, have been investigated. The ratio of Cl^- ions among the first neighbours around the cations, n_cl/(n_f+ n_cl) (= R_Cl) was calculated to investigate the distribution of Cl^- ions. The values of R_Cl of Zr⁴⁺ ions were similar to Cl^- contents in terms of anionic % in all the systems. r_cl's of Ba²⁺ ions were larger than those of Zr⁴⁺ ions. In the non-glass forming system containing MgCl₂, the Mg²⁺ ion showed larger values of r_cl than those of the Ca^Ca2+ and Sr²⁺ ions. In the system containing CaCl₂, the molecular dynamics calculations have been carried out on several different compositions which were located within, near the boundary and outside the glass forming region. The degrees of localization of Cl^- ions were calculated under some assumptions. The calculated degree of the localization were found to have some correlation with the glass forming tendency.