Local structure of network modifier to network former ions in soda‐lime alumino‐borosilicate glasses

The structure of soda‐lime alumino‐borosilicate glass was studied using molecular dynamics simulations of samples of varying compositions containing ~20 000 atoms each. Pair distribution functions ( PDF s) of cations to oxygen were used for comparison to available experimental data to evaluate consistency between simulations and experiment. Additional PDF s and coordination of the network forming cations (Al/B/Si) to network modifiers (Ca/Na) were examined, which is difficult to measure experimentally. The results are consistent with available experimental data regarding cation‐oxygen bond lengths and network former to oxygen coordination numbers. Si and Al are predominantly 4‐coordinated, with a small concentration of overcoordinated species similar to experimental data. B varied as 3‐coordinated, BO 3 , and 4‐coordinated, BO 4 , as a function of the amount of Ca 2+ and Na + present, the ratio of Al 2 O 3 to B 2 O 3 , and the fictive temperature of the sample, similar to experimental data. The simulations provide new information regarding the locations on the network modifiers to the +3 cations, Al and B. For instance, one Al ion can have multiple Na within 4 Å, but also the Na can be within 4 Å of several +3 cations. Such results would indicate a greater complexity of local structure that goes beyond the stoichiometric one +1 modifier ion near one +3 network former or one +2 modifier near two +3 formers in tetrahedral sites.