A neutron diffraction and Al-27 MQMAS NMR study of rare-earth phosphate glasses, (R2O3)(x)(P2O5)(1-x), x=0.187-0.263, R = Ce, Nd, Tb containing Al impurities

Cole, J.M. and van Eck, E.R.H. and Mountjoy, G. and Newport, R.J. and Brennan, T. and Saunders, G.A. (1999) A neutron diffraction and Al-27 MQMAS NMR study of rare-earth phosphate glasses, (R2O3)(x)(P2O5)(1-x), x=0.187-0.263, R = Ce, Nd, Tb containing Al impurities. Journal of Physics-Condensed Matter, 11 (47). pp. 9165-9178. ISSN 0953-8984. (Full text available)

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http://dx.doi.org/10.1088/0953-8984/11/47/304

Abstract

A neutron diffraction study of four rare-earth phosphate glasses of composition (R2O3)(x)(P2O5)(1-x), where x = 0.197, 0.235, 0.187, 0.263 and R = Ce, Ce, Nd, Tb respectively is presented. The structures of these materials were investigated as a function of (a) rare-earth atomic number and (b) composition. The results show that samples containing the larger rare-earth ions (Ce3+ and Nd3+) are coordinated to seven oxygen atoms whereas the immediate environment of Tb3+ ions is six coordinate. This implies that rare-earth clustering must be present in the samples containing larger rare-earth ions although no R...R correlations are directly observed. Terminal and bridging P-O correlations are resolved, existing in an approximately I:I ratio. Second-neighbour O(P)O separations are located with good accuracy and P(O)P correlations relating to the bridging chain are observed. There is also first evidence for the third neighbour correlation, P(OP)O, at similar to 2.8 Angstrom. A residual feature in the neutron diffraction data. present at similar to 1.8 Angstrom, is interpreted as Al-O correlations on the basis of Al-27 MQMAS NMR experiments. This aluminium impurity originates from the use of aluminium oxide crucibles used in the glass synthesis and is shown to exist as a mixture of octahedral, tetrahedral and penta-coordinated Al-O species. No structural perturbations of the overall network were observed with varying sample composition.

Item Type: Article
Subjects: Q Science
Divisions: Faculties > Science Technology and Medical Studies > School of Physical Sciences > Functional Materials Group
Depositing User: J.M. Smith
Date Deposited: 08 May 2009 16:15
Last Modified: 02 Dec 2011 11:52
Resource URI: http://kar.kent.ac.uk/id/eprint/15887 (The current URI for this page, for reference purposes)
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