PNNL

Abstract

The atomic structures of lithium, sodium and potassium silicate glasses spanning the glass formation range were studied using molecular dynamics simulations. The compositional dependence of the First Sharp Diffraction Peaks (FSDPs) and the contributions of partial structure factors to the FSDPs in these glasses were determined based on the calculated neutron static structure factors. The correlations of the FSDP with the short and medium range structure of these silicate glasses were examined. It is found that the position and the shape of FSDP strongly depend on the type and concentration of alkali oxide in alkali silicate glasses. The intermediate range order decreases with increasing alkali oxide concentration, as indicated by the decrease of the characteristic repeat distances and the characteristic correlation lengths. Lithium silicate glasses show anomaly in the characteristic correlation length, which increases with lithium oxide concentration. This anomaly is explained by the high field strength of lithium ions that increases the intermediate range order of the silicon oxygen network. The position and intensity of the FSDP are found to be mainly due to the structure features relating to the length range of 4-12 Å.