Molecular dynamic simulation on the structure of sodium germanate glasses

Citation
T. Nanba et al., Molecular dynamic simulation on the structure of sodium germanate glasses, J NON-CRYST, 277(2-3), 2000, pp. 188-206
Citations number
45
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science
Journal title
JOURNAL OF NON-CRYSTALLINE SOLIDS
ISSN journal
0022-3093 → ACNP
Volume
277
Issue
2-3
Year of publication
2000
Pages
188 - 206
Database
ISI
SICI code
0022-3093(200011)277:2-3<188:MDSOTS>2.0.ZU;2-M
Abstract
The structure of Na2O-GeO2 glasses has been investigated, using molecular d ynamics (MD) simulations based on an empirical three-body interaction model . A multi-body potential function with two energy minima in the angular ter m for a given three-atom unit was introduced to permit a transformation bet ween different coordination states, such as 4-and 6-fold coordinated Ce sit es. Parameters in the potential function were optimized with a non-linear l east-squares (NLS) method. The optimal parameter set obtained with a Na4Ge9 O20 crystal was employed for the structural models of pure GeO2 and 2Na(2)O . 9GeO(2) glasses. In the model for the binary glass, however, a number of 5-fold coordinated Ge, non-bridging O and 3-fold coordinated O formed. Ano ther binary model free from 5-fold Ge was prepared using a simple scheme in which no three-body interaction was applied to the structural units contai ning 5-fold coordinated Ge. All the structural models produced showed good agreement with the experiments, including vibrational spectra and radial di stribution functions (RDFs). No significant difference between the experime ntal observables of the two binary glass models was revealed, except for th e coordination environment of Ge. This is because 5- and B-fold Ge do not o ccur in a discrete arrangement through a corner-sharing of GeO4, e.g. GeO5. 6-GeO4-GeO5.6, but in a dense configuration, e.g. as edge-sharing GeO5.6-Ge O5.6, forming smaller rings than those in pure GeO2 glass. (C) 2000 Elsevie r Science B.V. All rights reserved.