The structure and properties of binary zinc phosphate glasses studied by molecular dynamics simulations

BC Tischendorf
TM Alam
RT Cygan
JU Otaigbe

Abstract

In recent years, the use of molecular dynamics (MD) simulations to understand and predict the properties of materials has become an increasingly popular and powerful tool. In this study, MD simulations were used to investigate the structural and physical properties of a binary zinc phosphate glass series, xZnO (.) (100 - x)P2O5, (40 less than or equal to x less than or equal to 70) where x is the mole percent modifier. A newly developed forcefield model incorporating Coulombic, plus two- and three-body interactions was employed, with the model parameters being empirically derived from known zinc-phosphate crystal structures. This zinc-phosphate forcefield model was used to perform MD calculations of densities, glass transition temperatures, T-g, average coordination numbers (CN) radial distribution functions, G(r), and pair distribution function, g(r), as a function of Zn concentration. In addition, the effects of computational quenching rates on the simulated densities were also investigated. Overall, the MD simulation results revealed the presence of long-range order in the form of rings and chains near the metaphosphate composition. These extended range structures disappeared beyond the metaphosphate composition, becoming isolated non-bridging phosphate tetrahedron as the Zn concentration approached the pyrophosphate composition. The MD simulations also revealed that the average Zn CN was invariant across the entire Zn concentration range investigated. These results demonstrate that the observed T-g behavior does not require an increase in the Zn CN. (C) 2003 Elsevier Science B.V. All rights reserved.