Structure of GeO2-P2O5 glasses studied by x-ray and neutron diffraction

U. Hoppe, R. K. Brow, B. C. Tischendorf, P. Jóvári, A. C. Hannon

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Abstract

The structures of three xGeO2-(1- x)P2O5 glasses, where x ≤ 0.98,0.88, and 0.81, have been studied by neutron and x-ray diffraction experiments that yield well resolved P-O and Ge-O bond distances. The Ge-O coordination number (NGeO) increased from 4.0 ± 0.2 to 4.5 ± 0.2 with the decrease in x from 0.98 to 0.81. The increase in NGeO is consistent with a structural model that assumes that all oxygen form Ge-O-Ge and P-O-Ge linkages between Ge polyhedra and P tetrahedra and that new GeO5 or GeO6 polyhedra are formed with isolated PO4 units when P2O5 is added to GeO2. The bond valencies in the P-O bonds of the PO4 tetrahedra are greater than unity and are balanced in P-O-Ge bridges with underbonded Ge-O links in the GeO5 or GeO6 polyhedra. Mixed site connections are expected for the GeO5 (or GeO6) and PO4 units in glasses with relatively low (<20 mol%) P 2O5 content due to the overwhelming fraction of GeO 4 tetrahedra. The structural changes are compared with those reported for alkali germanate glasses. Several features indicate different characteristics for the compositional dependence of NGeO for the GeO2-P2O5 and alkali germanate glasses. However, the distributions of the first-neighbour Ge-O distances are found to be nearly identical for the GeO2-P2O5 and K 2O-GeO2 glasses of equimolar K2O and P 2O5 content.

Original languageEnglish
Pages (from-to)1847-1860
Number of pages14
JournalJournal of Physics Condensed Matter
Volume18
Issue number6
DOIs
Publication statusPublished - Feb 15 2006

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ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics

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