Structure of Potassium Germanophosphate Glasses by X-ray and Neutron Diffraction: 2. Medium-range Order


Characteristics of the medium-range order (MRO) of K2O-GeO2-P2O5 (KGP) glasses are obtained from X-ray and neutron scattering data. The behavior of the MRO is expressed in changes of pre-peaks and smooth contributions in the structure factors, S(Q), for Q < 12 nm-1. Peaks at Q = (7.5 ± 0.5) nm-1 (Q - magnitude of the scattering vector) are the outstanding features and reach maximum intensity for a glass of not, vert, similar25/50/25 mol% K2O/GeO2/P2O5. The pre-peaks are explained by a structural model in which K-rich and Ge-rich regions are separated by PO4 units. The distance of repetition of similar regions (not, vert, similar1 nm) is responsible for the pre-peak at not, vert, similar7.5 nm-1. The intensity of this pre-peak is reduced and finally eliminated for glass compositions approaching the binary GeO2-P2O5 system. The pre-peak is changed to a smooth scattering contribution and finally shifted to not, vert, similar9 nm-1 for glass compositions approaching the binary K2O-GeO2 system. The strong tendency of the PO4 units to coordinate K+ and Ge neighbors at their four corners is the source for the special MRO of the KGP glasses.


Materials Science and Engineering


German Research Association
National Science Foundation (U.S.)

Keywords and Phrases

X-Ray Diffraction; Germanates; Medium-Range Order; Neutron Diffraction/Scattering; Oxide Glasses; Phosphates

International Standard Serial Number (ISSN)

0022-3093; 1873-4812

Document Type

Article - Journal

Document Version


File Type





© 2007 Elsevier, All rights reserved.

Publication Date

01 Jul 2007