Molecular dynamics simulation studies were made of lithium phosphate glasses having various Li2O contents. Two different P-O distances, corresponding to P coordination with bridging-O and non-bridging O, were identified. Non-bridging to bridging O interconversion, or bond switching, was noted. This resulted in the dynamic equilibration of tetrahedral phosphate units, Pn, where n = 1.3 indicated the number of bridging O atoms in the coordination of P. The non-bridging to bridging O bond switching was activated, with an effective activation energy of 0.03 to 0.05eV. The Li jumps did not appear to be strongly coupled to bond switching. The numbers of Li+ ions which were coordinated to an optimum number of non-bridging O atoms, and the numbers of Li+ ions which jumped out of their sites, appeared to be related. A detailed analysis was made of the dynamics of the Pn species, and new insights were obtained regarding ion migration in network-modified phosphate glasses.

Molecular Dynamics Study of Lithium Ion Conduction in Phosphate Glasses and the Role of Non-Bridging Oxygen. A.Karthikeyan, P.Vinatier, A.Levasseur, K.J.Roa: Journal of Physical Chemistry B, 1999, 103[30], 6185-92