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Molecular dynamics, diffraction and EXAFS of rare earth phosphate glasses compared with predictions based on bond valence

Mountjoy, Gavin (2007) Molecular dynamics, diffraction and EXAFS of rare earth phosphate glasses compared with predictions based on bond valence. Journal of Non-Crystalline Solids, 353 (18-21). pp. 2029-2034. ISSN 0022-3093. (doi:10.1016/j.jnoncrysol.2007.02.027) (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided) (KAR id:9912)

The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided.
Official URL:
http://dx.doi.org/10.1016/j.jnoncrysol.2007.02.027

Abstract

Rare earth (RE) phosphate glasses, (R2O3)(x)(P2O5)](1-x), commonly form with x < 0.3. As previously discussed by Hoppe, in this composition range Q(2) groups provide 6 O-nb (non-bridging oxygens) per RE, but higher RE coordinations can occur if RE are bonded to O-nb on Q(3) groups, or if RE-O-nb-RE configurations occur (where Q" refers to a PO4 tetrahedra with connectivity of n). The values of N-RO and R-RO from the majority of the previous diffraction and EXAFS studies of RE phosphate glasses have been surveyed. Overall, the experimental results for 0.18 <= x <= 0.28 indicate RE coordination is from 6.5 to 7.0 for large RE, and slightly lower for small RE. For x >= 0.23 this implies the occurrence of RE-O-nb-RE configurations, as observed in recent diffraction studies. The experimental results for x <= 0.15 indicate RE coordination is from 7.5 to 8, which can be attributed to RE bonding to O-nb on Q(3) groups. RE coordination of 8 for x similar to 0.15 requires 2 Q(3) groups (per RE) to be connected to Q(2) groups. Comparison with estimated connectivities between Q(2) and Q(3) groups indicate that chemically ordered Q(2)-Q(3) linkages are required. A recent MD model of a Tb metaphosphate glass has N-RO = 6, but includes Tb bonded to O-nb on Q(3) groups and Tb-O-nb-Tb configurations, because it has a broad Q" distribution.

Item Type: Article
DOI/Identification number: 10.1016/j.jnoncrysol.2007.02.027
Uncontrolled keywords: neutron diffraction/scattering; X-ray diffraction; molecular dynamics; phosphates; X-ray absorption
Subjects: Q Science
Divisions: Divisions > Division of Natural Sciences > Physics and Astronomy
Depositing User: Gavin Mountjoy
Date Deposited: 04 Jul 2008 13:02 UTC
Last Modified: 16 Nov 2021 09:48 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/9912 (The current URI for this page, for reference purposes)

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