New interaction potentials for alkaline earth silicate and borate glasses

Structure and properties of magnesium silicate and borate melts and glasses were investigated by using newly parameterized interaction potentials in molecular dynamics simulations and compared with those of calcium silicate and borate. The competition between the depolymerization of the silica network and the formation of new bonds with modifier ions leads to the enhancement of the elastic moduli with increasing modifier content in alkaline earth silicate glasses. Compared with calcium silicate, the higher elastic moduli of magnesium silicate result from a higher connectivity of the overall glass network due to the incorporation of fourfold coordinated magnesium and a more rigid connection between SiO4 tetrahedra and modifier ions. In contrast to the silicates, the effect of modifier content on the elastic moduli of alkaline earth borates is dominated by the fraction of fourfold coordinated boron (N4). Calcium borate with higher N4 shows a more rigid network structure and higher elastic moduli.