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Structure of Na₂O-GeO₂-P₂O₅ Glasses by X-Ray and Neutron Diffraction
Journal of Non-Crystalline Solids
  • Uwe Hoppe
  • N. P. Wyckoff
  • Richard K. Brow, Missouri University of Science and Technology
  • M. Von Zimmermann
  • A. C. Hannon
Abstract

Large fractions of six-coordinated Si are detected in Na2O-SiO2-P2O5 glasses with large P2O5 contents, and so six-coordinated Ge is expected in the structures of Na2O-GeO2-P2O5 (NGP) glasses with similar P2O5 contents. This behavior is investigated by X-ray and neutron diffraction. The Ge-O coordination numbers vary in the range 4.45 ≤ NGeO ≤ 5.6. Most GeO6 octahedra exist in the glass with the smallest GeO2 fraction (24 mol%). The Na+ ions are associated only with non-bridging oxygens (NBO) on phosphate tetrahedra, even though the ratio n(NBO)/n(Na) decreases from two for NaPO3 glass to ~ 1.3 for a glass with 37 mol% GeO2. The peak shape of the P-O distances changes strongly between NaPO3 and the NGP glass of 24 mol% but it is unchanged for the other NGP glasses. Atomistic models of the glasses with the maximum possible NGeO, with Na+ ions that find full charge compensation on NBO neighbors successfully reproduce the experimental NGeOs. The corresponding behavior is described by a general equation which is based on the mole fractions of Na2O, P2O5, and GeO2 and the ratio n(NBO)/n(Na). An earlier study of similar K2O-GeO2-P2O5 glasses with greater GeO2 content revealed the existence of strong pre-peaks in the scattering intensities at very small Q-values (7.5 nm-1). Here, similar pre-peaks are observed (at 8 nm-1) which are interpreted with an analogous model. Na-rich and Ge-rich phosphate nano-domains with distances of ~ 1.0 nm for repetition of like domains are assumed to explain the pre-peaks.

Department(s)
Materials Science and Engineering
Comments
This workwas supported in part by the National Science Foundation (DMR 0305202).
Keywords and Phrases
  • Germanium,
  • Neutron Diffraction,
  • Phosphates,
  • X Ray Diffraction, Charge Compensation,
  • Coordination Number,
  • General Equations,
  • Germanates,
  • Glass Structure,
  • Non-Bridging Oxygen,
  • Scattering Intensity,
  • X-Ray And Neutron Diffraction, Glass
Document Type
Article - Journal
Document Version
Citation
File Type
text
Language(s)
English
Rights
© 2014 Elsevier B.V., All rights reserved.
Publication Date
4-1-2014
Publication Date
01 Apr 2014
Citation Information
Uwe Hoppe, N. P. Wyckoff, Richard K. Brow, M. Von Zimmermann, et al.. "Structure of Na₂O-GeO₂-P₂O₅ Glasses by X-Ray and Neutron Diffraction" Journal of Non-Crystalline Solids Vol. 390 (2014) p. 59 - 69 ISSN: 0022-3093
Available at: http://works.bepress.com/richard-brow/202/