Molecular dynamics simulation of La2O3–Na2O–SiO2 glasses. I. The structural role of La3+ cations

It is well known that high-field strength rare-earth (RE) ions in the silicate glasses tend to cluster regardless of their concentration. Numerous experimental studies have been carried out, but the ability to discern structural information at the atomic-level strongly depends on providing accurate molecular dynamics (MD) simulations. In this work, the short- and medium-range order of La ion in soda silicate glasses is investigated by MD computer simulations. The glass mixtures used in these MD simulations are the same as those of a recent NMR study. Results of this study are in excellent agreement with the NMR results. It is found that the La cation has an average co-ordination of 6.5 O atoms with an average bond length fitted to be about 0.25 nm. The La is found to behave as a network modifier, and competes with sodium for non-bridging oxygen (NBO) atoms. In addition, the extended X-ray fine structure (EXAFS) and neutron diffraction patterns are predicted from the MD simulations.