Molecular dynamics simulations of the lithium coordination environment in phosphate glasses

A molecular dynamics (MD) study of the lithium ultraphosphate glass series, xLi(2)O .(1-x)P2O5 (0 less than or equal to x less than or equal to 0.5) w as used to investigate the changes in the Li environment with increasing mo difier concentration. The results from the MD simulations indicate that onl y gradual structural variations in the Li coordination environment occur as a function of modifier content. Changes in the type of oxygen coordinated to the Li are observed to correlate with the minimum in the glass transitio n temperature. Additionally, changes in the number of shared phosphorus ver tices were seen with increasing modifier concentration, in support of recen t models involving the role of the cation modifier in the extended range st ructure of phosphate glasses. Empirical calculations of the Li-6 NMR chemic al shifts directly from the MD simulation structures are also reported and compared to recent experimental solid-state NMR results.