Molecular dynamics simulation of the structure and properties of lithium phosphate glasses

A new forcefield model was developed for the computer simulation of phospha te materials. The model provides a fundamental basis for the evaluation of phosphate glass structure and thermodynamics, and was used to perform molec ular dynamics (MD) simulations of a series of lithium phosphate glass compo sitions (xLi(2)O . (1 - x)P2O5, 0 less than or equal to x less than or equa l to 0.5). Microstructural features and thermodynamic properties, as well a s their correlations with chemical compositions, were analyzed. An importan t structural feature observed for the phosphate glasses was the occurrence of ring structures that were related to the chemical composition. Relative stability of the ring structures with respect to the number of phosphate te trahedra within the ring was investigated using molecular orbital calculati ons on various phosphate conformations of clusters. An increase in stabilit y was observed as the ring size increases from two- to four-membered rings. A larger abundance of the smallest ring size, the 3-membered rings (P3O3), corresponds to the minimum of the glass transition temperature (T-g) in th e lithium phosphate glass series (corresponding to the composition 0.2Li(2) O . 0.8P(2)PO(5)). The impact of these strained 3-membered rings, along wit h the changes in the Li-coordination environment, on determining the spectr oscopic and thermodynamic properties of the phosphate glasses is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.