The molecular dynamics study of lithium ion conduction in phosphate glasses and the role of non-bridging oxygen

Abstract

Molecular dynamics (MD) simulation of lithium phosphate (Li₂O-P₂O₅) glasses with varying Li₂O content has been carried out. Two different P-O distances corresponding to phosphorus coordination with bridging oxygen (BO) and non-bridging oxygen (NBO) were identified in the simulated glasses. NBO-BO interconversion or bond switching was noted, which results in a dynamic equilibration of the tetrahedral phosphate units (Pⁿ, n = 1,3 indicates the number of bridging oxygen atoms in the coordination of phosphorus). The NBO-BO bond switching is mildly activated with an effective activation barrier of 0.03-0.05 eV. Lithium ion jumps do not appear to be strongly coupled to bond switching. But the number of Li⁺ ions coordinated to an optimum number of NBOs and the number of Li+ ions jumping out of their sites appear to be correlated. Detailed analysis was made of the dynamics of Pⁿ species and new insights have been obtained regarding ion migration in network-modified phosphate glasses.