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Neutron and Resonant X-ray Diffraction Studies of Zirconolite-2M

Published online by Cambridge University Press:  01 February 2011

Karl R. Whittle ,
Katherine L. Smith ,
Neil C. Hyatt  and
Gregory R. Lumpkin
Karl R. Whittle
Affiliation:
Institute of Materials Engineering, ANSTO, Private Mail Bag 1, Menai 2234, NSW, Australia Department of Engineering Materials, University of Sheffield, Sheffield, S1 3JD, UK
Katherine L. Smith
Affiliation:
Institute of Materials Engineering, ANSTO, Private Mail Bag 1, Menai 2234, NSW, Australia
Neil C. Hyatt
Affiliation:
Department of Engineering Materials, University of Sheffield, Sheffield, S1 3JD, UK
Gregory R. Lumpkin
Affiliation:
Institute of Materials Engineering, ANSTO, Private Mail Bag 1, Menai 2234, NSW, Australia
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Abstract

Zirconolite (nominally CaZrTi2O7) is a constituent phase of potential waste forms for the safe immobilisation of actinide wastes. Structural studies of such materials provide important information about cation ordering, lattice parameters, and strain effects, and provide input into the modelling of alpha decay damage and the development of future wasteform designs. A suite of zirconolites based on the replacement of Ti with Nb and Fe has been studied using high resolution neutron diffraction and resonant X-ray diffraction to determine the degree of disorder across the available cation sites. Resonant X-ray diffraction is a unique method which allows the location of certain cations to be determined accurately by taking advantage of the change in scattering power close to an absorption edge (e.g., Nb-K and Zr-K). Using standard X-ray diffraction alone this is not possible and there is little scattering difference between Nb and Zr.

Raman spectroscopy and measured lattice parameters have shown that the exchange of Ti with Nb and Fe has a non-linear effect on the unit cell dimensions and Raman peak positions while retaining the 2M polytype. Mössbauer spectroscopy has shown that the Fe preferentially fills the Ti split (C2) site. The results from this study provide a more complete picture of the cation order-disorder problem and are generally consistent with the behaviour of lattice parameters across the series.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1107: Scientific Basis for Nuclear Waste Management XXXI , 2008 , 331
Copyright
Copyright © Materials Research Society 2008

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